On-Chip Micro Temperature Controllers Based on Freestanding Thermoelectric Nano Films for Low-Power Electronics

Multidimensional integration and multifunctional com-ponent assembly have been greatly explored in recent years to extend Moore’s Law of modern microelectronics.However,this inevitably exac-erbates the inhomogeneity of temperature distribution in microsystems,making precise temperature control for electronic components extremely challenging.Herein,we report an on-chip micro temperature controller including a pair of thermoelectric legs with a total area of 50×50μm^(2),which are fabricated from dense and flat freestanding Bi2Te3-based ther-moelectric nano films deposited on a newly developed nano graphene oxide membrane substrate.Its tunable equivalent thermal resistance is controlled by electrical currents to achieve energy-efficient temperature control for low-power electronics.A large cooling temperature difference of 44.5 K at 380 K is achieved with a power consumption of only 445μW,resulting in an ultrahigh temperature control capability over 100 K mW^(-1).Moreover,an ultra-fast cooling rate exceeding 2000 K s^(-1) and excellent reliability of up to 1 million cycles are observed.Our proposed on-chip temperature controller is expected to enable further miniaturization and multifunctional integration on a single chip for microelectronics.

Wood-derived freestanding integrated electrode with robust interface-coupling effect boosted bifunctionality for rechargeable zinc-air batteries

Fabricating non-noble metal-based carbon air electrodes with highly efficient bifunctionality is big challenge owing to the sluggish kinetics of oxygen reduction/evolution reaction(ORR/OER).The efficient cathode catalyst is urgently needed to further improve the performance of rechargeable zinc-air batteries.Herein,an activation-doping assisted interface modification strategy is demonstrated based on freestanding integrated carbon composite(CoNiLDH@NPC)composed of wood-based N and P doped active carbon(NPC)and CoNi layer double hydroxides(CoNiLDH).In the light of its large specific surface area and unique defective structure,CoNiLDH@NPC with strong interfacecoupling effect in 2D-3D micro-nanostructure exhibits outstanding bifunctionality.Such carbon composites show half-wave potential of 0.85 V for ORR,overpotential of 320 mV with current density of 10 mA cm^(-2) for OER,and ultra-low gap of 0.70 V.Furthermore,highly-ordered open channels of wood provide enormous space to form abundant triple-phase boundary for accelerating the catalytic process.Consequently,zinc-air batteries using CoNiLDH@NPC show high power density(aqueous:263 mW cm^(-2),quasi-solid-state:65.8 mW cm^(-2))and long-term stability(aqueous:500 h,quasi-solid-state:120 h).This integrated protocol opens a new avenue for the rational design of efficient freestanding air electrode from biomass resources.

Freestanding oxide membranes:synthesis,tunable physical properties,and functional devices

The study of oxide heteroepitaxy has been hindered by the issues of misfit strain and substrate clamping,which impede both the optimization of performance and the acquisition of a fundamental understanding of oxide systems.Recently,however,the development of freestanding oxide membranes has provided a plausible solution to these substrate limitations.Single-crystalline functional oxide films can be released from their substrates without incurring significant damage and can subsequently be transferred to any substrate of choice.This paper discusses recent advancements in the fabrication,adjustable physical properties,and various applications of freestanding oxide perovskite films.First,we present the primary strategies employed for the synthesis and transfer of these freestanding perovskite thin films.Second,we explore the main functionalities observed in freestanding perovskite oxide thin films,with special attention to the tunable functionalities and physical properties of these freestanding perovskite membranes under varying strain states.Next,we encapsulate three representative devices based on freestanding oxide films.Overall,this review highlights the potential of freestanding oxide films for the study of novel functionalities and flexible electronics.

Porous nitrogen-enriched hollow carbon nanofibers as freestanding electrode for enhanced lithium storage

Onedimensional porous carbons bearing high surface areas and sufficient heteroatom doped functionalities are essential for advanced electrochemical energy storage devices,especially for developing freestanding film electrodes.Here we develop a porous,nitrogenenriched,freestanding hollow carbon nanofiber(PNFHCF)electrode material via filtration of polypyrrole(PPy)hollow nanofibers formed by in situ selfdegraded templateassisted strategy,followed by NH3assisted carbonization.The PNFHCF retains the freestanding film morphology that is composed of threedimensional networks from the entanglement of 1D nanofiber and delivers 3.7fold increase in specific surface area(592 m^(2)g^(-1))compared to the carbon without NH_(3)treatment(FHCF).In spite of the enhanced specific surface area,PNFHCF still exhibits comparable high content of surface N functionalities(8.8%,atom fraction)to FHCF.Such developed hierarchical porous structure without sacrificing N doping functionalities together enables the achievement of high capacity,highrate property and good cycling stability when applied as selfsupporting anode in lithiumion batteries,superior to those of FHCF without NH3 treatment.

Electrochemical liftoff of freestanding GaN by a thick highly conductive sacrificial layer grown by HVPE

Separation technology is an indispensable step in the preparation of freestanding GaN substrate. In this paper, a largearea freestanding GaN layer was separated from the substrate by an electrochemical liftoff process on a sandwich structure composed of an Fe-doped GaN substrate, a highly conductive Si-doped sacrificial layer and a top Fe-doped layer grown by hydride vapor phase epitaxy(HVPE). The large difference between the resistivity in the Si-doped layer and Fe-doped layer resulted in a sharp interface between the etched and unetched layer. It was found that the etching rate increased linearly with the applied voltage, while it continuously decreased with the electrochemical etching process as a result of the mass transport limitation. Flaky GaN pieces and nitrogen gas generated from the sacrificial layer by electrochemical etching were recognized as the main factors responsible for the blocking of the etching channel. Hence, a thick Si-doped layer grown by HVPE was used as the sacrificial layer to alleviate this problem. Moreover, high temperature and ultrasonic oscillation were also found to increase the etching rate. Based on the results above, we succeeded in the liftoff of ~ 1.5 inch GaN layer. This work could help reduce the cost of freestanding GaN substrate and identifies a new way for mass production.

Highly Dispersive Co@N-C Catalyst as Freestanding Bifunctional Cathode for Flexible and Rechargeable Zinc–air Batteries

The design of efficient cathode with great cycle performance,high flexibility,and low cost is essential for the commercialization of zinc–air battery(ZAB).Herein,we report the exploration of freestanding bifunctional cathode with rationally designed structures,namely,tiny Co nanoparticles embedded in Ndoped carbon nanofiber aerogels,which have desired features including uniform Co dispersity,balanced distribution of N-C species,hierarchically porous structure with increased fraction of meso-to micropores,and moderate amounts of defects.Accordingly,the as-fabricated cathodes exhibit positive half-wave potential of 0.82 V for oxygen reduction and small overpotential of 350 mV at 10 mA cm^(−2) for oxygen evolution,respectively,which deliver smaller reversible oxygen electrode index(0.76 V)than the commercial Pt/C+RuO_(2)(0.80 V)and most Co-based electrocatalysts ever reported.Impressively,the as-constructed liquid rechargeable ZAB behaves high peak power density(160 mW cm^(−2)),large specific capacity(759.7 mAh g^(−1) at 10 mA cm^(−2),tested after 120 h of OCV tests),and robust stability over 277 h.Moreover,the as-assembled quasi-solid-state ZAB using such freestanding cathode represents excellent mechanical flexibility and outstanding cycle performance,regardless of being serviced under extremely bending conditions from 0°to 180°,underscoring their promising applications as durable bifunctional cathode for portable metalair batteries.

Green Fabrication of Freestanding Piezoceramic Films for Energy Harvesting and Virus Detection

Most electronics such as sensors,actuators and energy harvesters need piezoceramic films to interconvert mechanical and electrical energy.Transferring the ceramic films from their growth substrates for assembling electronic devices commonly requires chemical or physical etching,which comes at the sacrifice of the substrate materials,film cracks,and environmental contamination.Here,we introduce a van der Waals stripping method to fabricate large-area and freestanding piezoceramic thin films in a simple,green,and cost-effective manner.The introduction of the quasi van der Waals epitaxial platinum layer enables the capillary force of water to drive the separation process of the film and substrate interface.The fabricated lead-free film,Ba_(0.85)Ca_(0.15)Zr_(0.1)Ti_(0.9)O_(3)(BCZT),shows a high piezoelectric coefficient d_(33)=209±10 pm V−1 and outstanding flexibility of maximum strain 2%.The freestanding feature enables a wide application scenario,including micro energy harvesting,and covid-19 spike protein detection.We further conduct a life cycle analysis and quantify the low energy consumption and low pollution of the water-based stripping film method.

Freestanding fibers assembled by CoPSe@N-doped carbon heterostructures as an anode for fast potassium storage in hybrid capacitors

Although the fast development of potassium-ion hybrid capacitors(PIHC)recently,the issues such as the slow kinetics and poor durability of potassium ion hosts greatly restric their applications.Herein,a freestanding fiber(NHF fiber)with necklace-like configuration and CoPSe@N-doped carbon(CoPSe@NCNT)heterostructured units is introduced as the anode in PIHC.The highly porous network of NHF fiber facilitates the fast ion transports and promises the good high-rate property.Additionally,the nanoscle crystallites inside in-situ grown NCNT favor the high adaption to volume expansion/shrinkage and endow good structure stability during ion insertion/deinsertion.Density function theoretical(DFT)calculations disclose the CoPSe@NCNT heterostructure has improved intrinsic conductivity,fast potassium migration,and decreased energy barrier.Meanwhile,the finite element simulation analysis(FEA)reveals the decreased stress inside the NHF architecture during charge/discharge processes.Moreover,the electrochemical tests confirm the fast and durable properties of the CoPSe@NCNT NHF fibers for potassium storage.Furthermore,the PIHC full cell with the anode of CoPSe@NCNT NHF fiber is assembled,which obtains the superior energy/power densities and high capacity retention(89%)after 2000 cycles at 2 A g^(-1).When the polymer electrolyte is incooperated,the flexible PIHC device achieves the good pliability and good adaptation during wide temperature changes from-20 to 25℃.Therefore,this work introduces a novel anode for fast potassium ion storage,and opens a new approach to assemble the power sources for flexible electronics in diverse conditions.

Growth and Electronic Application of p-Undoped Freestanding Diamond Film

P-type undoped freestanding diamond （FSD） films were grown by the microwave plasma chemical vapor deposition （MPCVD） method. The effects of the hydrogen plasma treat- ment and annealing process on the p-type behavior of FSD films were investigated by the Hall effect method. The results revealed that the sheet carrier concentration increased and the sheet resistivity decreased with the treating time and a stable value was achieved after a period of time. Up to an annealing temperature of 250℃, the sheet resistivity and sheet carrier concentration remained in a relatively stable range but changed dramatically after annealing at 300℃. A heterojunction was also fabricated by the growth of an n-type ZnO film on the p-type FSD film. Current-voltage （I-V） characterization of the heterojunction at room temperature indicated that this structure was rectifying in nature with a turn-on voltage of about 0.6 V.

Enhanced ferromagnetism and conductivity of ultrathin freestanding La_(0.7)Sr_(0.3)MnO_(3)membranes

We report a universal method to transfer freestanding La_(0.7)Sr_(0.3)MnO_(3)membranes to target substrates.The 4-unit-cell-thick freestanding La_(0.7)Sr_(0.3)MnO_(3)membrane exhibits the enhanced ferromagnetism,conductivity and out-of-plane magnetic anisotropy,which otherwise shows nonmagnetic/antiferromagnetic and insulating behavior due to the intrinsic epitaxial strain.This work facilitates the promising applications of ultrathin freestanding correlated oxide membranes in electronics and spintronics.

Flame Aerosol Synthesis of Freestanding ZnO Nanorods

ZnO can be made into many nanostructures that have unique properties for advanced applications, such as piezoelectric and pyroelectric materials. ZnOnanorod is one of the nanostructures that possess advanced properties. This paper reports a gas phase flame process to continuously synthesize aerosols of ZnOnanorods in large quantities. Unlike previous work, our process shows that pure ZnOnanorods can be made in a freestanding form rather than growing on a substrate surface. It was found that the ZnOnanorods preferentially grow in the thermodynamically stable direction [001] in the gas phase with different aspect ratios, depending on flame process conditions. The ZnOnanorod aerosols are highly crystalline and have a hexagonal geometry. Raman and photoluminescence spectroscopic studies showed that there are no structural defects in the nanorods, which have energy band gap of 3.27 eV in the near UV region. It was demonstrated that the gas phase flame reactor can provide a convenient means for continuous production of highly pure aerosols of ZnOnanorods.

Direct Process to Prepare Crystallized Freestanding Membranes of Hydroxyapatite Using Sacrificial Layer of Barium-Compounds

Freestanding membrane (FSM) of hydroxyapatite (HA) is a thin sheet of pure HA without any supporting substrates. Our original preparation process of FSM of HA had three steps: The first was the deposition of HA layer on sacrificial layer of solvent-soluble materials, the second was separation of FSM of HA by means of dissolution of sacrificial layer, and the third was post-annealing to crystallize FSM of HA. To date, the post-annealing process was a serious bottleneck of productivity owing to its too long time. In this short report, we proposed a novel sacrificial layer, heatproof and water-soluble Ba-compound, which makes the direct deposition of crystallized HA possible due to its heatproof property because the problem on the original process was that the previous sacrificial layers have no heatproof property and HA layer should be deposited as amorphous. We can deposit the Ba-compound sacrificial layer only in 1 hour followed with the direct deposition of crystallized HA layer, substituting the 20 hours of post-annealing. The FSM of HA was separated successfully from the substrate by means of dissolution of Ba-compound with water. Our novel process can shrink the process time by 19 hours.

Hetero-Epitaxy and Self-Adaptive Stressor Based on Freestanding Fin for the 10 nm Node and Beyond

A promising technology named epitaxy on nano-scale freestanding fin （ENFF） is firstly proposed for hetero- epitaxy. This technology can effectively release total strain energy and then can reduce the probability of gener- ating mismatch dislocations. Based on the calculation, dislocation defects can be eliminated completely when the thickness of the Si freestanding fin is less than 10nm for the epitaxial Ge layer. In addition, this proposed ENFF process can provide sufficient uniaxial stress for the epitaxy layer, which can be the major stressor for the SiGe or Ge channel fin field-effect transistor or nanowire at the 10nm node and beyond. According to the results of technology computer-aided design simulation, nanowires integrated with ENFF show excellent electrical perfor- mance for uniaxial stress and band offset. The ENFF process is compatible with the state of the art mainstream technology, which has a good potential for future applications.

Freestanding MoSe_(2)nanoflowers for superior Li/Na storage properties

MoSe_(2),with high theoretical specific capacity,has attracted a lot of attention.There remains an open challenge to effectively suppress the irreversible selenium dissolution and rapid capacity decrease induced by severe volume change during cycling.Herein,we synthesize MoSe_(2)nanoflowers dispersed on one-dimensional(1D)N-doped carbon nanofibers(MoSe_(2)@NCNFs)for use as a freestanding electrode.In this unique structure,the 1D N-doped carbon nanofibers are found to not only enhance the conductivity but also ensure the structural integrity during the Li^(+)/Na^(+)insertion/destraction processes.As expected,at 2 A·g^(-1),the specific capacity of the MoSe_(2)@NCNFs is maintained at 180 mAh·g^(-1)after 500 cycles when used in lithium storage applications.Furthermore,in the case of sodium storage,at 1 A·g^(-1),the MoSe_(2)@NCNFs shows a capacity of 122mAh·g^(-1)after 500 cycles.These findings suggest that the MoSe_(2)@NCNF electrodes may be a promising candidate for use in reversible Li/Na storage applications.

Freestanding 1T MoS_(2)@MXene hybrid film with strong interfacial interaction for highly reversible zinc ions storage

Aqueous zinc ion batteries(AZIBs)are now gaining widespread attention because of their costeffectiveness,intrinsic saf ety,and high theoretical capacity.Nevertheless,it is still crucial to exploit highperformance electrode materials.Herein,the freestanding 1T MoS_(2)@Mxene hybrid films(MMHF)were synthesized and directly served as the cathode of AZIBs.The freestanding MMHF exhibited the hierarchical layer structure with excellent conductivity and strong interfacial interaction,which promoted the exposure of more active sites and the transfer of electrons/ions.Consequently,the MMHF displayed a high specific capacity of 270 mAh g^(-1)(at 0.1 A g^(–1))and good rate performance.Impressively,even after 2500 cycles under 10 A g^(-1),the freestanding MMHF cathode contributed a superior specific capacity of 108 mAh g^(-1)with an outstanding capacity retention rate of 94.7%.Meanwhile,the energy storage mechanism of the MMHF electrode was also elucidated through ex-situ characterizations.Furthermore,the density functional theory(DFT)computations revealed the strong interfacial interactions between 1T MoS_(2)and MXene,high conductivity,and low Zn^(2+)diffusion barrier.This work provides a new viewpoint for designing freestanding transition metal disulfides(TMDs)-MXene hybrid film electrodes for AZIBs.

High conductive graphene assembled films with porous micro-structure for freestanding and ultra-low power strain sensors

Graphene emerges as an ideal material for constructing high-performance strain sensors,due to its superior mechanical property and high conductivity.However,in the process of assembling graphene into macroscopic materials,its conductivity decreases significantly.Also,tedious fabrication process hinders the application of graphene-based strain sensors.In this work,we report a freestanding graphene assembled film(GAF)with high conductivity((2.32±0.08)×105 S m-1).For the sensitive materials of strain sensors,it is higher than most of reported carbon nanotube and graphene materials.These advantages enable the GAF to be an ultra-low power consumption strain sensor for detecting airflow and vocal vibrations.The resistance of the GAF remains unchanged with increasing temperature(20-100℃),exhibiting a good thermal stability.Also,the GAF can be used as a strain sensor directly without any flexible substrates,which greatly simplifies the fabrication process in comparison with most reported strain sensors.Additionally,the GAF used as a pressure sensor with only^4.7μW power is investigated.This work provides a new direction for the preparation of advanced sensors with ultra-low power consumption,and the development of flexible and energy-saving electronic devices.

Porous carbon framework nested nickel foam as freestanding host for high energy lithium sulfur batteries

Constructing 3 D multifunctional conductive framework as stable sulfur cathode contributes to develop advanced lithium-sulfur(Li-S)batteries.Herein,a freestanding electrode with nickel foam framework and nitrogen doped porous carbon(PC)network is presented to encapsulate active sulfur for Li-S batteries.In such a mutually embedded architecture with high stability,the interconnected carbon network and nickel foam matrix can expedite ionic/electro nic tra nsport and sustain volume variations of sulfur.Furthermore,rationally designed porous structures provide sufficient internal space and large surface area for high active sulfur loading and polar polysulfides anchoring.Benefiting from the synergistic superiority,the Ni/PC-S cathode exhibits a high initial capacity of around 1200 mAh/g at 0.2 C,excelle nt rate perfo rmance,and high cycling stability with a low decay rate of 0.059%per cycle after 500 cycles.This work provides a useful strategy to exploit freestanding porous framework for diverse applications.

Freestanding strontium vanadate/carbon nanotube films for long-life aqueous zinc-ion batteries

Aqueous rechargeable zinc-ion battery(ZIB)is considered to be a potential energy storage system for large-scale applications due to its environmental friendliness,high safety,and low cost.However,it remains challenging to develop suitable cathode materials with high specific capacity and long-term cyclic stability.Herein,we have fabricated freestanding Sr0.19V2O51.3H2O/carbon nanotubes(SrVO/CNTs)composite films with different mass ratios by incorporating SrVO into CNTs network.The synthesized SrVO possesses a large interlayer spacing of 1.31 nm,which facilitates Zn(2+)diffusion.Furthermore,the SrVO/CNTs composite film with conductive network structure promotes electron transfer and ensures good contact between SrVO and CNTs during the long-term cycling process.As a result,the battery based on the SrVO/CNTs composite cathode with a mass ratio of 7:3 delivers a specific capacity of 326 mAh·g^(-1)at 0.1 A·g^(-1)and 145 mAh·g^(-1)at 5 A·g^(-1),demonstrating a high capacity and excellent rate capability.Remarkably,the assembled ZIB shows good capacity retention of 91%even after ultra-long cycling for 7500 cycles at a high current rate of 5 Ag^(-1).More importantly,the battery also delivers a high energy density and power density,as 290 Wh·kg^(-1)at 125 W·kg^(-1)(0.1 A·g^(-1)),or 115 Wh·kg^(-1)at 6078 W·kg^(-1)(5 Ag^(-1)).The results demonstrate that the SrVO/CNTs composite is a promising cathode toward large-scale energy storage applications.

Sb nanoparticles encapsulated in N-doped carbon nanotubes as freestanding anodes for high-performance lithium and potassium ion batteries

Sb-based materials with high specific capacity have targeted as an alternative anode material for alkali metal ion batteries.Herein,Sb nanoparticles embedded in hollow porous N-doped carbon nanotubes(Sb@N-C nanotubes)are used as freestanding anode for Li-ion batteries(LIBs)and K-ion batteries(PIBs).The Sb@N-C nanotubes demonstrate exceptional reversible capacity of643 mAh·g^(-1)at 0.1 A·g^(-1)with long cycle stability,as well as outstanding rate performance(219.6 mAh·g^(-1)at10 A·g^(-1))in LIBs.As the anode material of PIBs,they reveal impressive capacity of 325.4 mAh·g^(-1)at 0.1 A·g^(-1).The superior electrochemical properties mainly originate from the novel structure.To be specific,the obtained 3D connected network allows for quick ion and electron migration,and prevents the aggregation of Sb nanoparticles.The hollow porous nanotubes can not only accommodate the volume expansion of Sb nanoparticles during cycling,but also facilitate the infiltration of the electrolyte and reduce the ion diffusion length.This work provides a new insight for designing advanced Sb-based anodes for alkali metal ion batteries.

Freestanding MXene-based macroforms for electrochemical energy storage applications

Freestanding MXene-based macroforms have gained significant attention as versatile components in electrochemical energy storage applications owing to their interconnected conductive network,strong mechanical strength,and customizable surface chemistries derived from MXene nanosheets.This comprehensive review article encompasses key aspects related to the synthesis of MXene nanosheets,strategies for structure design and surface medication,surface modification,and the diverse fabrication methods employed to create freestanding MXene-based macroform architectures.The review also delves into the recent advancements in utilizing freestanding MXene macroforms for electrochemical energy storage applications,offering a detailed discussion on the significant progress achieved thus far.Notably,the correlation between the macroform’s structural attributes and its performance characteristics is thoroughly explored,shedding light on the critical factors influencing efficiency and durability.Despite the remarkable development,the review also highlights the existing challenges and presents future perspectives for freestanding MXenebased macroforms in the realms of high-performance energy storage devices.By addressing these challenges and leveraging emerging opportunities,the potential of freestanding MXene-based macroforms can be harnessed to enable groundbreaking advancements in the field of energy storage.