Beom Joon Kim

Tufts University | Tufts · Department of Biomedical Engineering

Water-based processing plays a crucial role in high technology, especially in electronics, material sciences and life sciences, with important implications in the development of high-quality reliable devices, fabrication efficiency, safety and sustainability. At the micro- and nanoscale, water is uniquely enabling as a bridge between biological and...

The quest for flexible curvilinear displays is driving renewed interest in natural soft photonic systems that rely on the adaptable response of nanostructured living tissues to external stimuli for camouflage and energy management. Understanding and controlling the dynamics of these systems is challenging due to difficulties in sourcing the tissues...

Structurally colored materials, which rely on the interaction between visible light and nanostructures, produce brilliant color displays through fine control of light interference, diffraction, scattering, or absorption. Rationally combining different color‐selective functions into a single form offers a powerful strategy to create programmable opt...

Natural systems display sophisticated control of light-matter interactions at multiple length scales for light harvesting, manipulation, and management, through elaborate photonic architectures and responsive material formats. Here, we combine programmable photonic function with elastomeric material composites to generate optomechanical actuators t...

We performed infrared transmission experiment on ion-gel gated graphene and measured carrier scattering rate g as function of carrier density n over wide range up to n=2E13 cm-2. The g exhibits a rapid decreases along with the gating followed by persistent increases on further carrier doping. This behavior of g(n) demonstrates that carrier is scatt...

Significance Silk polymorphism is used to generate composite materials that can wrinkle reversibly and in complex patterns. This is achieved by leveraging and controlling the ability of structural proteins to change their conformation and their stimulus-responsive behavior to offer a different approach to micro/nanopatterning of dynamic, multifunct...

We performed infrared transmission experiment on ion-gel gated graphene and measured carrier scattering rate γ as a function of carrier density n over a wide range up to n = 2 × 10 ¹³ cm ⁻² . γ exhibits a rapid decrease along with the gating followed by a persistent increase upon further carrier doping. This behavior of γ(n) demonstrates that the c...

The first use of proton conductors for gating graphene transistors is demonstrated. The proton conductor used in this study, [poly(styrenesulfonic acid)], is added with sodium halide salts in order to improve the capacitive characteristics of the electrolyte gate dielectric. The influence of the added sodium halide salts (NaF, NaCl, NaBr, and NaI),...

High-performance vertical field-effect transistors based on graphene electrodes doped are developed using the underside doping method. The underside doping method enables effective tuning of the graphene work function while maintaining the surface properties of the pristine graphene.

On page 5875, J. H. Cho and co-workers demonstrate a new device architecture for flexible vertical Schottky barrier (SB) transistors and logic gates based on graphene–organic-semiconductor–metal heterostructures and ion gel gate dielectrics. The devices show well-behaved p- and n-type characteristics under low-voltage operation (<1 V), yielding hig...

A new device architecture for flexible vertical Schottky barrier (SB) transistors and logic gates based on graphene-organic-semiconductor-metal heterostructures and ion gel gate dielectrics are demonstrated. The devices show well-behaved p- and n-type characteristics under low-voltage operation (<1 V), yielding high current densities (>100 mA cm(-2...

The piezopotential-powered active matrix strain sensor array based on piezopotential-gated graphene transistor (GT) is demonstrated using a piezoelectric polymer. The strain sensor based on piezopotential-gated GT exhibits excellent performances including ultrahigh sensitivity (gauge factor = 389) and good durability (>3000 bending and releasing cy...

Solution-gated graphene transistors were developed recently for use in pH sensor applications. The device operation is understood to rely on the capability of hydronium and hydroxide ions in solution to change the electrical properties of graphene. However, hydronium and hydroxide ions are accompanied by other ionic species in a typical acidic or b...

Organic field-effect transistor (OFET) memories have rapidly evolved from low-cost and flexible electronics with relatively low-memory capacities to memory devices that require high-capacity memory such as smart memory cards or solid-state hard drives. Here, we report the high-capacity OFET memories based on the multilayer stacking of densely packe...

Water, the primary electrolyte in biology, attracts significant interest as an electrolyte-type dielectric material for transistors compatible with biological systems. Unfortunately, the fluidic nature and low ionic conductivity of water prevents its practical usage in such applications. Here, we describe the development of a solid state, megahertz...

We demonstrate photo-patternable ion gel-gated graphene transistors and inverters on plastic substrates. The photo-patternable ion gel can be used as a negative photoresist for the patterning of underlying graphene as well as gate dielectrics. As a result, an extra graphene-patterning step is not required, which simplifies the device fabrication an...

Organic field-effect transistor (OFET) memory devices made using highly stable iron-storage protein nanoparticle (NP) multilayers and pentacene semiconductor materials are introduced. These transistor memory devices have nonvolatile memory properties that cause reversible shifts in the threshold voltage (Vth ) as a result of charge trapping and det...

An In/Ga-free doping method of zinc oxide (ZnO) is demonstrated utilizing a printable charge transfer doping layer (CTDL) based on (3-aminopropyl)triethoxysilane (APS) molecules. The self-assembled APS molecules placed on top of ZnO thin-films lead to n-type doping of ZnO and filling shallow electron traps, due to the strong electron-donating chara...

We characterized the electrical properties of ambipolar polymer field-effect transistors (PFETs) based on the low-band-gap polymer, pNAPDO-DPP-EH. The polymer consisted of electron-rich 2,6-di(thienyl)naphthalene units with decyloxy chains (NAPDO) and electron-deficient diketopyrrolopyrrole units with 2-ethylhexyl chains (DPP-EH). The as-spun pNAPD...

We investigated electrical charge transport through individual strands of single-crystalline dipentyl perylene tetracarboxylic diimide (PTCDI-C5) and dioctyl perylene tetracarboxylic diimide (PTCDI-C8) nanowires prepared by a solution-phase self-assembly method. Temperature-dependent mobility measurements (100–280 K) revealed distinct electrical tr...

Controlled alignment and patterning of individual semiconducting nanowires at a desired position in a large area is a key requirement for electronic device applications. High-speed, large-area printing of highly aligned individual nanowires that allows control of the exact numbers of wires, and their orientations and dimensions is a significant cha...

The structural, electrical and optical properties of high-performance, low-temperature and solution-processed alkali metal-doped ZnO TFTs were studied using various analytic instruments, including HR-TEM, AFM, XPS, EDS, electrical bias stability test and UV-vis spectroscopy. Furthermore, we successfully demonstrated that a change in the optical ban...

Fast and reproducible patterning of high-resolution rGO microstructures over a large area directly on various substrates by modulating the surface energy is reported. The pattern formation of rGO thin films is based on the difference in the adhesion strength between the mold/rGO and rGO/substrates interfaces. Such highly defined rGO micropatterns a...

We present systematic control of the crystallinity and electrical transport properties of C60 films that are deposited onto pentacene layers, based on simple tuning of the underneath pentacene layer thickness. With increasing the pentacene layer thickness from 0 to 2 monolayers, we observed improvement in crystallinity and grain size of the C60 lay...

We demonstrated that the viscoelasticity of a dielectric surface affected the overlying pentacene crystalline nanostructures and the electrical performances of pentacene-based field-effect transistors (FETs). The surface viscoelasticities of the gate dielectrics were systematically controlled by varying the polymer chain lengths of polystyrene brus...

The environmentally friendly reduction and a solution processability of chemically modified graphene nanosheets are most important for their applications. Here we report for the first time that in situ synthesis of hydrazine and spontaneous reduction of graphene oxide (GO) in solution can be achieved just by addition of hexamethyldisilazane (HMDS)...

A facile method for achieving optical switching of the Dirac point and conductance in reduced graphene oxide multilayer FETs that are non-covalently functionalized with a photo-responsive spiropyran derivative is presented. The photoresponsive transition from spiropyran to merocyanine induces the reversible optical switching in graphene based FETs.

Transparent flexible graphene transistors and inverters in a coplanar-gate configuration were presented for the first time using only two materials: graphene and an ion gel gate dielectric. The novel device configuration simplifies device fabrication such that only two printing steps were required to fabricate transistors and inverters. The devices...

The device performance and stability of n-type organic field-effect transistors (OFETs) based on 1,2,3,7,8,9-hexafluoro-indeno[1,2-b]fluorene-6,12-dione (TriF-IF-dione) were investigated. The electrical characteristics of TriF-IF-dione FETs were optimized by systematically controlling the dielectric surface properties via insertion of organic inter...

Transfer characteristics of ZnO thin-film transistors (TFTs) based on ZnO doped with various alkali metals. A new doping method is demonstrated by employing alkali metals to achieve high-performance and solution-processed ZnO TFTs with a low processing temperature (similar to 300 degrees C), which is applicable to flexible plastic substrates.

Transfer characteristics of ZnO thin-film transistors (TFTs) based on ZnO doped with various alkali metals. A new doping method is demonstrated by employing alkali metals to achieve high-performance and solution-processed ZnO TFTs with a low processing temperature (∼300 °C), which is applicable to flexible plastic substrates

Wrinkle-free reduced graphene oxide (rGO)/TiO(2) hybrid multilayer films were directly fabricated using an rGO solution stabilized by a TiO(2) precursor sol applied over a large area by an air spraying method without the use of additional reduction processes. In-situ insertion of the TiO(2) layer between rGO sheets dramatically increased the conduc...

With the emergence of human interface technology, the development of new applications based on stretchable electronics such as conformal biosensors and rollable displays are required. However, the difficulty in developing semiconducting materials with high stretchability required for such applications has restricted the range of applications of str...

We have developed solution-processed reduced graphene oxide (RGO) transistors with ion gel gate dielectrics. The combination of solution-processed high-capacitance ion gel gate dielectrics and spraycoated RGO films yielded high-performance RGO transistors that operated below 4 V. Two reduction processes were applied to GO: (i) chemical reduction by...

We developed high-performance stable n-type organic field-effect transistors (OFETs) using indenofluorenediones with different numbers of fluorine substituents (MonoFIF- dione, DiF-IF-dione, and TriF-IF-dione). Top-contact OFETs were fabricated via the vacuum deposition of indenofluorenediones as the semiconducting channel material on polystyrenetr...

A high-performance low-voltage graphene field-effect transistor (FET) array was fabricated on a flexible polymer substrate using solution-processable, high-capacitance ion gel gate dielectrics. The high capacitance of the ion gel, which originated from the formation of an electric double layer under the application of a gate voltage, yielded a high...

Low voltage high mobility n-type thin film transistors �TFTs� based on sol-gel processed zinc oxide �ZnO� were fabricated using a high capacitance ion gel gate dielectric. The ion gel gated solution-processed ZnO TFTs were found to exhibit excellent electrical properties. TFT carrier mobilities were 13 cm2 /V s, ON/OFF current ratios were 105, rega...