Inkjet Printing Technique Research Articles

Method for controlling the polypropylene wettability using surfactants

This paper describes a novel approach to imaging polypropylene PP using digital inkjet printing techniques. The low surface energy of PP, and significant hydrophobic properties prevent it from being used for direct coloration by available methods. A number of surfactants (surfactants) have been proposed as pre-coatings to improve the adhesion between the polymer surface and the ink. Due to the amphiphilicity of surfactants, improved coloration and enhanced color rendering are provided. The polymer/surfactants interactions were evaluated by IR spectroscopy. The amount of surfactants was evaluated using TGA analysis. The effect of modifying agent concentration was evaluated using wetting edge angle measurement. The surface morphology was evaluated using scanning electron microscopy. The test scales were printed and their colorimetric performance was investigated. The study demonstrates the high potential of surfactants for tuning the properties of nonwoven polymeric materials.

Inkjet Printing of a Gate Insulator: Towards Fully Printable Organic Field Effect Transistor

In this work, a gate insulator poly (4-vinylphenol) (PVP) of an organic field effect transistor (OFET) was deposited using an inkjet printing technique, realized via a high printing resolution. Various parameters, including the molecular weight of PVP, printing direction, printing voltage, and drop frequency, were investigated to optimize OFET performance. Consequently, PVP with a smaller molecular weight of 11 k and a printing direction parallel to the channel, a printing voltage of 18 V, and a drop frequency of 10 kHz showed the best OFET performance. With a direct ink writing-printed organic semiconductor, this work paves the way for fully inkjet-printed OFETs.

Interphase-Controlled Inkjet Printing of MicroInlaid OLEDs: Effects of Solvent- and Solute-Polymer Interactions.

Inkjet printing, a highly promising technique for the cost-effective fabrication of large-scale organic light-emitting devices (OLEDs), typically necessitates the intricate alignment of precisely patterned insulating layers. Recently, we introduced a unique single-step inkjet printing process that produces well-patterned microinlaid spots of functional compounds through insulating polymer layers. This approach exploits lateral phase separation between the solute of functional compounds and the polymer, allowing the simultaneous spatial etching of the polymer and the infilling of the solute using a single inkjet-printed sessile droplet. Here, we demonstrate that the interaction between the solvent and polymer, as well as the solute and polymer, critically determines the precision and efficiency of printing. This is particularly evident when using either the insulating poly(vinylpyridine) isomer of poly(4-vinylpyridine) (P4VP) or poly(2-vinylpyridine) (P2VP) with chloroform as a solvent, which allows for a detailed examination of these interactions based on certain solubility parameters. Micro-Raman spectroscopy reveals that the self-organizing capability of the microinlaid spots with P4VP is superior to that with P2VP. This is due to the fact that P2VP shows higher affinity to the solvent and causes imperfect phase separation as compared to P4VP. As a result, a performance evaluation demonstrates enhanced device performance for inkjet-printed green micro-OLEDs with P4VP, exhibiting a higher external quantum efficiency of 3.3% compared to that of 2.3% achieved with P2VP. These findings elucidate the important roles of solvent-polymer and solute-polymer interactions in the inkjet printing process, leading to interfacial control of inkjet printing technique for the cost-effective production of high-performance and high-resolution micro-OLEDs.

Microdrop InkJet printed supercapacitors of graphene/graphene oxide ink for flexible electronics

The inkjet printing (IJP) technique is a highly promising technology for fabricating flexible electronics for wearable applications. The latest Microdrop IJP technology was introduced to produce flexible supercapacitors using a readily prepared graphene/graphene oxide ink. Molecular modelling concepts were conducted prior to ink formulation to investigate the interaction between graphene and GO via adsorption interactions to investigate the feasibility of adding GO to G for energy storage processes. Calculations validate that their interaction yields stable, highly reactive, and conductive structures. Molecular electrostatic potential maps reveal excellent charge distribution proposing G/GO as a potential candidate for electrochemical processes. Subsequently, GNPs/GO blend was prepared, leveraging the electric conductivity and high surface area of graphene, and the functional groups in GO to enhance graphene dispersion. Simple and interdigitated supercapacitor electrodes were fabricated without further post-printing complexities. The highly flexible interdigitated supercapacitor (100L) demonstrated notable performance with areal capacitance of 195.1 F m−2 at 0.4 A.m−2, power density of 1199.34 mW m−2, energy density of 24.91 mWh.m−2, and 80.65 % capacitance retention after 5000 cycles. The outstanding electrocapacitive performance was ascribed to GO's abundant functional groups and its 3D open structure. These factors contribute to adding a pseudocapacitive effect and enhancing charge transfer within the electrode channel-like networks.

Direct-Written Silver Electrodes for All-Solution-Processed Low-Voltage Organic Thin Film Transistors Towards Flexible Electronics Applications

Recent progress inprinted electronics has offered the possibility of fabricatingvarious organic-based electronic devices,such as organic light-emitting diodes (OLEDs) and organic thin film transistors (OTFTs).As one of the important deposition methods inprinted electronics, an inkjet printing technique offers the deposition of solution-processable materials onto a variety of substrates using simpler fabrication steps at lower processing temperatures, which is suitable for flexible electronic applications. Despite being the leading choice in OTFT fabrication,the clogging issues that frequently occurred at the printhead nozzle havenot only limitedthe material selection but also restrained the efforts to bring organic electronic devices to the market. Apart from that, although remarkable progress has been made to enhance the performance of the OTFT, the high operating voltage resulting from the low gate capacitance density of the inorganic oxide-based dielectric layer remains a critical limitation that hinders the practical application of the OTFT. Hence, in this paper, we propose a simple solution-based method to develop a low-voltageOTFT. This work utilized a direct-write printing technique to print silver source/drain and gate electrodes incorporated into a bottomgate bottom contact OTFT structure, a spin-coating deposition method to deposit both small molecule TIPS-pentacene organic semiconducting layer and high-kPVA dielectric layer. Notably, the proposed OTFT achieved a micrometre channel length with a saturation mobility of 4.49 × 10-1cm2/Vs, a threshold voltage of -1.5V, an on/off current ratio of 108, and a subthreshold swing of 66.8mV/dec whilethe overall fabrication temperature and operating voltage arekept below 150 °Cand -15 V, respectively.The direct ink writing technology incorporated into the high-kdielectric layer provides a new strategy to fabricate organic-related components,particularly the OFTFs at lower manufacturing cost and temperature towardsflexible and low-operating voltage electronic devices.

Printed flexible solid-state microsupercapacitor with highly-stable aqueous cobalt-based inks

Cobalt-based nanomaterials are among the most noticed candidates for manufacturing supercapacitive electrodes. Inkjet-printing is an emerging technique for fabricating miniaturized devices. In this work, highly flexible microsupercapacitors (MSCs) are manufactured, using a pseudocapacitive (C = 900 F‌ g−1 at 1 A g−1) Co-oxide-hydroxide water-based and ultra-stable (up to 12 months) ink on paper. The synthesized capacitive active material consists of cobalt-oxide nanocubes and cobalt-hydroxide hexagonal nanoflakes. Conductive (Rs = 13 Ω/□) silver nanowire networks serve as current collectors, and the morphology of cobalt oxide-hydroxide structures and the developed ink features, allow for printing well-detailed and homogeneous patterns. The inkjet-printed symmetric and asymmetric devices show notable areal specific capacitances of 35.68 mF cm−2 and 23.60 mF cm−2 at a current density of 0.1 mA cm−2, respectively. The asymmetric devices deliver impressive energy and power densities of 2.76 μW h cm−2 (4.10 W h kg−1) and 646 μW cm−2 (959 W kg−1), respectively. A thorough study on the cyclic and mechanical stability of the flexible devices resulted in perfect capacitance maintenance of 94.3 % after 10,000 charge and discharge cycles and retention of over 80 % even after 1000 cycles of successive bending and folding. The extensive study of capacitance retention following folding under various obtuse and reflex angles, which can be regarded as an important step toward characterizing flexible devices suitable for being utilized in wearable electronics, is carried out for the first time to the best of our knowledge. The findings of this study clearly illustrate the prospects of using the inkjet-printing technique to fabricate high-performance MSC devices appropriate for integration with flexible and wearable electronics.

Inkjet Printing Photoresist with Ultralow Viscosity on Silicon Wafers for Uniform Coating.

Inkjet printing is introduced into the photoresist coating process for uniform photoresist film formation on silicon wafers with the in-house inkjet experimental prototype. The optimization of a dual negative voltage waveform is proposed to achieve stable droplet jetting for the ultralow viscosity (0.71 mPa·s) photoresist with a 1:10 dilution ratio employed in the semiconductor packaging processes. Moreover, the maximum droplet jetting velocity can reach 9.51 m/s, and the droplet volume is controlled at ∼6.5 pL with excellent droplet concentration. The uniform film of the AZ P4620 photoresist is coated on silicon wafers by quantitatively exploring and optimizing the printhead driving frequency and movement velocity utilizing the droplet deposition model and experimental analysis. Results show that the optimal inkjet parameters with 5 kHz in jetting frequency and 6 mm/s in motion velocity can obtain a film evenness index of 4.81% with the thickness of 0.945 μm, which exhibits a more uniform photoresist film than the spray coating method. The study not only expands the application of the inkjet printing technique but also offers an alternative for photoresist coating in the photolithography process.

A Precursor-Derived Ultramicroporous Carbon for Printing Iontronic Logic Gates and Super-Varactors.

A liquid precursor for 3D printing ultramicroporous carbons (pore width <0.7nm) to create a novel in-plane capacitive-analog of semiconductor-based diodes (CAPodes) is presented. This proof-of-concept integrates functional EDLCs into microstructured iontronic devices. The working principle is based on selective ion-sieving, controlling the size of the electrolyte ions, and the nanoporous sieving carbon's pore size. By blocking bulky electrolyte ions from entering the sub-nanometer pores, a unidirectional charging characteristic with controllable ion flux is achieved, leading to diodic U-I characteristics with a high rectification ratio. The liquid precursor approach enables successful printing of miniaturized in-plane CAPodes. A combination of inkjet and extrusion printing techniques with suitable inks is explored to fabricate electrode materials with engineered porosity. Deliberate fine-tuning of the ultramicroporous carbon's porosity and surface area is achieved using a customized carbon precursor and CO2 etching techniques. Electrochemical evaluation of the printed CAPodes demonstrates successful miniaturization compared with macroscopic film assembly. 3D manufacturing and miniaturization allow for the integration of CAPodes into logic gate circuits (OR, AND). For the first time, these switchable devices are used as variable capacitors in a high-pass filter application, adjusting the cut-off frequency of applied alternating voltage analogous to an I-MOS varactor.

Inkjet printed IGZO memristors with volatile and non-volatile switching

Solution-based memristors deposited by inkjet printing technique have a strong technological potential based on their scalability, low cost, environmentally friendlier processing by being an efficient technique with minimal material waste. Indium-gallium-zinc oxide (IGZO), an oxide semiconductor material, shows promising resistive switching properties. In this work, a printed Ag/IGZO/ITO memristor has been fabricated. The IGZO thickness influences both memory window and switching voltage of the devices. The devices show both volatile counter8wise (c8w) and non-volatile 8wise (8w) switching at low operating voltage. The 8w switching has a SET and RESET voltage lower than 2 V and − 5 V, respectively, a retention up to 105 s and a memory window up to 100, whereas the c8w switching shows volatile characteristics with a low threshold voltage (Vth < − 0.65 V) and a characteristic time (τ) of 0.75 ± 0.12 ms when a single pulse of − 0.65 V with width of 0.1 ms is applied. The characteristic time alters depending on the number of pulses. These volatile characteristics allowed them to be tested on different 4-bit pulse sequences, as an initial proof of concept for temporal signal processing applications.

Printing of liquid metal by electrically modulating of interface tension in liquid environment

In recent years, gallium-based liquid metal has emerged as a prominent research material in the realm of flexible electronics, owing to its exceptional electrical conductivity and deformability. The crux of developing flexible electronic devices using liquid metal as a conductive material lies in the patterning of the liquid metal. Inkjet printing technology possesses the capability to efficiently craft functional patterns by printing any inkable material. However, due to the facile oxidation of the gallium-based liquid metal surface in ambient air, leading to the formation of oxide films and the presence of high surface tension, conventional inkjet printing techniques are incapable of directly rendering liquid metal prints. This manuscript introduces a refined and remarkably efficient approach to inkjet printing utilizing the liquid metal. By deftly adjusting the interfacial tension of the liquid metal at the nozzle with ultra-low potentials, falling within the 2-V range, the achievement of on-demand, micron-scale liquid metal microdroplet ejection printing surpassing 3 kHz is brought to fruition. This article delves into unraveling the mechanisms of potential modulation on the interfacial tension of the liquid metal at the nozzle, as well as the fundamental theories pertaining to the formation and migration of liquid metal microdroplets. These insights establish a theoretical and technical foundation for the application of liquid metals in the field of electronic printing.

Comparative analysis of X‐band FSS fabricated by inkjet printing and conventional etching technique

AbstractAn investigation of a single‐layer band‐stop frequency selective surface (FSS) is designed and analyzed for X‐band application. The proposed FSS design primarily involves a cross‐shaped conductive patch with four square slots on each corner, and it is fabricated on the 3D‐printed polylactic acid (PLA) substrate. The design is resonating at 12 GHz with an insertion loss greater than 60 dB. The 10 dB bandwidth of the designed structure is 8.3% with respect to the resonant frequency. The results show that the design has polarization‐independent and angle‐insensitive transmission characteristics for incidence angles up to 60°. The simulation is carried out using CST Microwave Studio Suite, and the results are obtained. The physical mechanism of the designed structure is evaluated using the surface current distribution. The designed FSS is fabricated using two techniques, namely inkjet printing and conventional etching. Finally, the measurements of the fabricated structure are done using a vector network analyzer setup.

A facile approach to fabricate dual-responsive smart natural fibre sensors

Smart textiles with the characteristics of lightweight, flexibility, deformability, and breathability have been around for some decades. Although natural fibres have these qualities naturally, the intelligence of natural fibres is still a challenge. This study provides a facile approach to prepare dual-responsive natural cellulose and wool fibres based on reversible acidichromic and photoisometric water-soluble polymeric dye. An acidichromic and photoiscomeric waterborne polyurethane reactive dye (PUD) with the chromaticity, further reactive groups, and waterborne macromolecular structure was first designed and subsequently synthesized via a diazo coupling reaction between a polyurethane precursor (PUP) and a para-ester diazonium salt (PDS). The synthesized PUD with the characteristics of a polyurethane backbone, azobenzene chromophore, β-sulfatoethylsulfone reactive groups, and waterborne sodium sulfate groups was applied in dying of natural fibre products including cotton, ramie and wool fibres with an excellent colour fastness. The PUD possesses a thermal stability and solvent resistance. The synthesized PUD and its dyed natural fibres displayed the acidichromic and photoisomeric behaviours. The maximum absorption peak of the PUD aqueous solution shifted from 442 nm to 503 nm due to the structural transition changing from diazo to hydrazone when the pH values were adjusted from 7 to 1. Meanwhile, the colour of PUD aqueous solution and its dyed cotton, ramie and wool fibres reversibly changed from yellow to red upon pH changing from 7 to 1. With being exposed to 365 nm UV light, the trans-isomers in PUD slowly transformed into cis-isomers with an isomerization rate of 7.68 × 10−5 s−1. The stimuli-responsive polyurethane reactive dye can be a promising candidate for the design of a wearable and flexible natural fibre sensors aiming for monitoring the changes of environment. Furthermore, the conductive and rheological behaviours of PUD aqueous solution exhibited a promising application in the preparation of smart textile sensors via ink-jet printing technique.

Multifunctional Micromachines Constructed by Combining Multiple Protein-Based Components with Different Functions.

Untethered mobile micromachines have considerable potential to realize more effective and minimally invasive medicine. Although diverse medical micromachines have been reported over the past few decades, these machines were developed for performing only specific tasks and the functions imparted to them were limited to a few. Hence, the methodologies for imparting a wide variety of functions to machines have not been fully explored. In this study, a novel construction strategy for the multifunctional micromachines is presented, where a specific function can be added to the machine in one step by directly combining the protein-based component, possessing the biological function of constituent proteins, to an arbitrary position of the machine by using an inkjet printing technique. As a proof-of-concept demonstration, various types of machines were constructed by combining multiple components with different functions. These constructed machines successfully performed functions as diverse as enzyme-powered self-propulsion, collection of target objects, including the bilirubin and living cells, enzyme-mediated conversion of substrate molecules to different ones, magnetic guidance, and release of anti-inflammatory drug diapocynin. The study's progressive approach as well as multifunctional and biocompatible machines composed of proteins will profoundly impact the development of intelligent machines equipped with multiplex sophisticated functionalities.

Toward Highly Efficient Solution‐Processable OLEDs: Inkjet Printing of TADF Emissive Layer

AbstractThe fabrication of optoelectronic devices using low‐cost inkjet printing techniques is a topic of great interest to the scientific and industrial community and represents a step toward the full deployment of solution‐processable organic light emitting diodes (OLEDs), particularly for commercial lighting and signaling applications. Herein, the inkjet printing of tBuCzDBA (9,10‐bis(4‐(3,6‐di‐tert‐butyl‐9H‐carbazol‐9‐yl)−2,6‐dimethylphenyl)−9,10‐diboraanthracene) is reported, a high‐performing thermally activated delayed fluorescence (TADF) emitter for OLEDs. Optimizing the surface tension values of the ink formulations and the associated wetting behavior are crucial parameters for achieving a uniform and homogeneous printed thin film. In particular, it is observed that using a proper mixture of solvents with different surface tensions, it is possible to generate Marangoni flows inside the drop, which triggers a very fast drying process, ensuring optimized morphological and optical properties in the inkjet printed tBuCzDBA‐based film. OLEDs exploiting this film as an emissive layer are then fabricated, achieving a maximum luminance of 32 000 cd m−2, a current efficiency of 27.5 cd A−1, and an external quantum efficiencyof 10%. To the best of the knowledge, this is the highest efficiency reported to date for self‐hosted TADF inkjet‐printed OLEDs.

Large-Area Flexible Perovskite Light-Emitting Diodes Enabled by Inkjet Printing.

Metal halide perovskite light-emitting diodes (PeLEDs) are attracting increasing attention due to their potential applications in flat panel lighting and displays. The solution process, large-area fabrication, and flexibility are attractive properties of PeLEDs over traditional inorganic LEDs. However, it is still very challenging to deposit uniform perovskite films on flexible substrates using a blade or slot-die coating, as the flexible substrate is not perfectly flat. Here, the inkjet printing technique is adopted, and the key challenges are overcome step-by-step in preparing large-area films on flexible substrates. Double-hole transporting layers are first used and a wetting interfacial layer to improve the surface wettability so that the printed perovskite droplets can form a continuous wet film. The fluidic and evaporation dynamics of the perovskite wet layer is manipulated to suppress the coffee ring effect by solvent engineering. Uniform perovskite films are obtained finally on flexible substrates with different perovskite compositions. The peak external quantum efficiency of the inkjet-printed PeLEDs reaches 14.3%. Large-area flexible PeLEDs (4×7 cm2 ) also show very uniform emission. This work represents a significant step toward real applications of large-area PeLEDs in flexible flat-panel lighting.

Research on the preparation of colloidal photonic crystals and the anti-counterfeiting applications

Anti-counterfeiting materials based on colloidal photonic crystals (PCs) have been widely studied due to their inimitable structural color and adjustable photonic band gap (PBG). And the patterned colloidal photonic crystals have been well applied in the field of anti-counterfeiting because of their easy preparation, high performance, and functionalization. The methods for preparing patterned colloidal photonic crystals are outlined, including vertical deposition, spin coating, spraying, and inkjet printing techniques. In this paper, the applications of patterned photonic crystals in the anti-counterfeiting field and their advantages are discussed, the future development of patterned photonic crystals and the challenges they face are also prospected.

Plasmon-Enhanced Perovskite Solar Cells Based on Inkjet-Printed Au Nanoparticles Embedded into TiO2 Microdot Arrays.

The exceptional property of plasmonic materials to localize light into sub-wavelength regimes has significant importance in various applications, especially in photovoltaics. In this study, we report the localized surface plasmon-enhanced perovskite solar cell (PSC) performance of plasmonic gold nanoparticles (AuNPs) embedded into a titanium oxide (TiO2) microdot array (MDA), which was deposited using the inkjet printing technique. The X-ray (XRD) analysis of MAPI (methyl ammonium lead iodide) perovskite films deposited on glass substrates with and without MDA revealed no destructive effect of MDA on the perovskite structure. Moreover, a 12% increase in the crystallite size of perovskite with MDA was registered. Scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HR-TEM) techniques revealed the morphology of the TiO2_MDA and TiO2-AuNPs_MDA. The finite-difference time-domain (FDTD) simulation was employed to evaluate the absorption cross-sections and local field enhancement of AuNPs in the TiO2 and TiO2/MAPI surrounding media. Reflectance UV-Vis spectra of the samples comprising glass/TiO2 ETL/TiO2_MDA (ETL-an electron transport layer) with and without AuNPs in TiO2_MDA were studied, and the band gap (Eg) values of MAPI have been calculated using the Kubelka-Munk equation. The MDA introduction did not influence the band gap value, which remained at ~1.6 eV for all the samples. The photovoltaic performance of the fabricated PSC with and without MDA and the corresponding key parameters of the solar cells have also been studied and discussed in detail. The findings indicated a significant power conversion efficiency improvement of over 47% in the PSCs with the introduction of the TiO2-AuNPs_MDA on the ETL/MAPI interface compared to the reference device. Our study demonstrates the significant enhancement achieved in halide PSC by utilizing AuNPs within a TiO2_MDA. This approach holds great promise for advancing the efficiency and performance of photovoltaic devices.

A comparison of conductive ink usage optimization techniques used in fabrication of epidermal UHF radio frequency identification tags for medical and sensing applications.

The aim of this work is to assess the performance of various inkjet printing techniques. These techniques are aimed at optimizing the volume of conductive ink used in the fabrication of inkjet printed Radio Frequency Identification tags. It is also possible that they can be used in fabricating other electronic and electromagnetic devices and structures. Three ink optimization approaches were examined viz. gridded (meshed) designs, conductive area trimming and selective ink deposition. The volume of conductive ink utilized in tag fabrication and the measured on-body (forearm) read range of the tag were used to develop a figure of merit which determined the best printing approach. Although the longest read range was obtained from the tag with 48% conductive area trimming (Trim 1), the best figure of merit, that is, the tag with the best balance between measured read range and utilized conductive ink, was obtained from the tag that had its surface area trimmed by 65% (Trim 2). It is however suggested that optimum use of conductive ink would be achieved with a combination of 65% surface area trimming and selective ink deposition technique.

Influence of Composite Thickness on Ultrasonic Guided Wave Propagation for Damage Detection Using Embedded PZT Transducers

This paper describes a study that focuses on assessing the influence of composites with different thicknesses (2 mm, 4 mm, and 9 mm) on embedded ultrasonic guided waves (UGWs) under varying temperatures. The study also demonstrates the effectiveness of these embedded sensors in identifying damage. A novel cut-out method that included an embedded diagnostic layer and phased-array lead zirconate titanate (PZT) transducers, created using the ink-jet printing technique in the manufacturing process was employed. The research then focused on studying the behavior of UGWs under varying temperatures for each composite panel. This analysis aimed to understand how temperature variations affected the propagation of guided waves in thick composites. Finally, artificial damage on the surface and impact damage were introduced, both embedded and surface-mounted PZT transducers were used to detect and locate these damages in different thickness composite panels. The results of damage localization indicated that the embedded PZT transducers were more sensitive than the surface-mounted transducers in locating the damage in thick composites.

Biomaterial-Based Biomimetic Visual Sensors: Inkjet Patterning of Bacteriorhodopsin.

Biomimetic visual sensors utilizing bacteriorhodopsin (bR) were fabricated by using an inkjet method. The inkjet printer facilitated the jetting of the bR suspension, allowing for the deposition of bR films. The resulting inkjet-printed bR film exhibited time-differential photocurrent response characteristics similar to those of a dip-coated bR film. By adjusting the number of printed bR film layers, the intensity of the photocurrent could be easily controlled. Moreover, the inkjet printing technique enabled unconstrained patterning, facilitating the design of various visual information processing functions, such as visual filters. In this study, we successfully fabricated two visual filters, namely, a two-dimensional Difference of Gaussian (DOG) filter and a Gabor filter. The printed DOG filter demonstrated edge detection capabilities corresponding to contour recognition in visual receptive fields. On the other hand, the printed Gabor filter proved effective in detecting objects of specific sizes as well as their motion and orientation. The integration of bR and the inkjet method holds significant potential for the widespread implementation of highly functional biomaterial-based visual sensors. These sensors have the capability to provide real-time visual information while operating in an energy-efficient manner.