Atypical self-activation of Ga dopant for Ge nanowire devices

Nanoscale doping of polymeric semiconductors with confined electrochemical ion implantation

Nanoresolved doping of polymeric semiconductors can overcome scaling limitations to create highly integrated flexible electronics, but remains a fundamental challenge due to isotropic diffusion of the dopants. Here we report a general methodology for achieving nanoscale ion-implantation-like electrochemical doping of polymeric semiconductors. This approach involves confining counterion electromigration within a glassy electrolyte composed of room-temperature ionic liquids and high-glass-transition-temperature insulating polymers. By precisely adjusting the electrolyte glass transition temperature (Tg) and the operating temperature (T), we create a highly localized electric field distribution and achieve anisotropic ion migration that is nearly vertical to the nanotip electrodes. The confined doping produces an excellent resolution of 56 nm with a lateral-extended doping length down to as little as 9.3 nm. We reveal a universal exponential dependence of the doping resolution on the temperature difference (Tg - T) that can be used to depict the doping resolution for almost infinite polymeric semiconductors. Moreover, we demonstrate its implications in a range of polymer electronic devices, including a 200% performance-enhanced organic transistor and a lateral p-n diode with seamless junction widths of <100 nm. Combined with a further demonstration in the scalability of the nanoscale doping, this concept may open up new opportunities for polymer-based nanoelectronics.

Nonlinear elastic aspects of multi-component iron oxide core-shell nanowires by means of atom probe tomography, analytical microscopy, and nonlinear mechanics

One-dimensional objects as nanowires have been proven to be building blocks in novel applications due to their unique functionalities. In the realm of magnetic materials, iron-oxides form an important class by providing potential solutions in catalysis, magnetic devices, drug delivery, or in the field of sensors. The accurate composition and spatial structure analysis are crucial to describe the mechanical aspects and optimize strategies for the design of multi-component NWs. Atom probe tomography offers a unique analytic characterization tool to map the (re-)distribution of the constituents leading to a deeper insight into NW growth, thermally-assisted kinetics, and related mechanisms. As NW-based devices critically rely on the mechanical properties of NWs, the appropriate mechanical modeling with the resulting material constants is also highly demanded and can open novel ways to potential applications. Here, we report a compositional and structural study of quasi-ceramic one-dimensional objects: α-Fe ⊕ α-FeOOH(goethite) ⊕ Pt and α-Fe ⊕ α-Fe₃O₄(magnetite) ⊕ Pt core-shell NWs. We provide a theoretical model for the elastic behavior with terms accounting for the geometrical and mechanical nonlinearity, prior and subsequent to thermal treatment. The as-deposited system with a homogeneous distribution of the constituents demonstrates strikingly different structural and elastic features than that of after annealing, as observed by applying atom probe tomography, energy-dispersive spectroscopy, analytic electron microscopy, and a micromanipulator nanoprobe system. During annealing at a temperature of 350 °C for 20 h, (i) compositional partitioning between phases (α-Fe, α-Fe₃O₄ and in a minority of α-Fe₂O₃) in diffusional solid-solid phase transformations takes place, (ii) a distinct newly-formed shell formation develops, (iii) the degree of crystallinity increases and (iv) nanosized precipitation of evolving phases is detected leading to a considerable change in the description of the elastic material properties. The as-deposited nanowires already exhibit a significantly large maximum strain (1-8%) and stress (3-13 GPa) in moderately large bending tests, which become even more enhanced after the annealing treatment resulting at a maximum of about 2.5-10.5% and 6-18 GPa, respectively. As a constitutive parameter, the strain-dependent stretch modulus undoubtedly represents changes in the material properties as the deformation progresses.

In Situ Transmission Electron Microscopy Analysis of Copper-Germanium Nanowire Solid-State Reaction

A promising approach of making high quality contacts on semiconductors is a silicidation (for silicon) or germanidation (for germanium) annealing process, where the metal enters the semiconductor and creates a low resistance intermetallic phase. In a nanowire, this process allows one to fabricate axial heterostructures with dimensions depending only on the control and understanding of the thermally induced solid-state reaction. In this work, we present the first observation of both germanium and copper diffusion in opposite directions during the solid-state reaction of Cu contacts on Ge nanowires using in situ Joule heating in a transmission electron microscope. The in situ observations allow us to follow the reaction in real time with nanometer spatial resolution. We follow the advancement of the reaction interface over time, which gives precious information on the kinetics of this reaction. We combine the kinetic study with ex situ characterization using model-based energy dispersive X-ray spectroscopy (EDX) indicating that both Ge and Cu diffuse at the surface of the created Cu₃Ge segment and the reaction rate is limited by Ge surface diffusion at temperatures between 360 and 600 °C. During the reaction, germanide crystals typically protrude from the reacted NW part. However, their formation can be avoided using a shell around the initial Ge NW. H_a direct Joule heating experiments show slower reaction speeds indicating that the reaction can be initiated at lower temperatures. Moreover, they allow combining electrical measurements and heating in a single contacting scheme, rendering the Cu-Ge NW system promising for applications where very abrupt contacts and a perfectly controlled size of the semiconducting region is required. Clearly, in situ TEM is a powerful technique to better understand the reaction kinetics and mechanism of metal-semiconductor phase formation.

Nanowire Electronics: From Nanoscale to Macroscale

Semiconductor nanowires have attracted extensive interest as one of the best-defined classes of nanoscale building blocks for the bottom-up assembly of functional electronic and optoelectronic devices over the past two decades. The article provides a comprehensive review of the continuing efforts in exploring semiconductor nanowires for the assembly of functional nanoscale electronics and macroelectronics. Specifically, we start with a brief overview of the synthetic control of various semiconductor nanowires and nanowire heterostructures with precisely controlled physical dimension, chemical composition, heterostructure interface, and electronic properties to define the material foundation for nanowire electronics. We then summarize a series of assembly strategies developed for creating well-ordered nanowire arrays with controlled spatial position, orientation, and density, which are essential for constructing increasingly complex electronic devices and circuits from synthetic semiconductor nanowires. Next, we review the fundamental electronic properties and various single nanowire transistor concepts. Combining the designable electronic properties and controllable assembly approaches, we then discuss a series of nanoscale devices and integrated circuits assembled from nanowire building blocks, as well as a unique design of solution-processable nanowire thin-film transistors for high-performance large-area flexible electronics. Last, we conclude with a brief perspective on the standing challenges and future opportunities.

Electrical characterization and examination of temperature-induced degradation of metastable Ge0.81Sn0.19 nanowires

Metastable germanium-tin alloys are promising materials for optoelectronics and optics. Here we present the first electrical characterization of highly crystalline Ge_0.81Sn_0.19 nanowires grown in a solution-based process. The investigated Ge_0.81Sn_0.19 nanowires reveal ohmic behavior with resistivity of the nanowire material in the range of ∼1 × 10^-4Ω m. The temperature-dependent resistivity measurements demonstrate the semiconducting behavior. Moreover, failure of devices upon heating to moderate temperatures initiating material degradation has been investigated to illustrate that characterization and device operation of these highly metastable materials have to be carefully conducted.

The ion implantation-induced properties of one-dimensional nanomaterials

Nowadays, ion implantation is an extensively used technique for material modification. Using this method, we can tailor the properties of target materials, including morphological, mechanical, electronic, and optical properties. All of these modifications impel nanomaterials to be a more useful application to fabricate more high-performance nanomaterial-based devices. Ion implantation is an accurate and controlled doping method for one-dimensional nanomaterials. In this article, we review recent research on ion implantation-induced effects in one-dimensional nanostructure, such as nanowires, nanotubes, and nanobelts. In addition, the optical property of single cadmium sulfide nanobelt implanted by N+ ions has been researched.

In Situ Real-Time TEM Reveals Growth, Transformation and Function in One-Dimensional Nanoscale Materials: From a Nanotechnology Perspective

This paper summarises recent developments in in situ TEM instrumentation and operation conditions. The focus of the discussion is on demonstrating how improved understanding of fundamental physical phenomena associated with nanowire or nanotube materials, revealed by following transformations in real time and high resolution, can assist the engineering of emerging electronic and optoelectronic devices. Special attention is given to Si, Ge, and compound semiconductor nanowires and carbon nanotubes (CNTs) as one of the most promising building blocks for devices inspired by nanotechnology.