Phase-change Films Research Articles

Shape-stabilized flexible thermochromic films with one-sided adhesion via gradient crosslinking strategy for temperature indicating

Thermochromic dyes (TCDs) based on a three-component color change system suffer from solid rigidity and liquid leakage issues because of the intrinsic solid–liquid phase change performance, resulting in difficulty in temperature visualization applications for smart wearable fields. Despite considerable efforts in microencapsulation of thermochromic dyes, designing and fabricating essentially flexible thermochromic phase change films still need to be explored. Herein, a one-sided adhesive gradient-crosslinked thermochromic film is reported to address these issues to make a trade-off between stability and flexibility, excellent thermochromic performance, and temperature visualization. The thermochromic wearable films have been fabricated exploiting tea polyphenol thermochromic dyes, vinyl dimethylsiloxane, and hydrosilicone oil via the salt-template-assisted method and gradient crosslinking strategy, which have porous structures with an average pore size of 12.8 μm and a porosity of 28 %. Due to the spatial limiting threshold effect of the porosity structure, interconnected 3D polysiloxane porous networks can provide ample support for tea polyphenol thermochromic dyes and effectively prevent liquid leakage. Upon heating, the thermochromic film changes from blue to white with the K/S value decreasing from 7.69 to 0.78 and the ΔE* increasing from 2.7 to 16.1 at 610 nm, and the color-changing temperature is 42 °C. Gradient crosslinked thermochromic films exhibit excellent temperature-responsive color change properties, desirable one-side adhesion, and thermal energy storage, enabling multicolor temperature displays and temperature-controlled multilevel information transfer.

Solution-derived Ge–Sb–Se–Te phase-change chalcogenide films

Ge–Sb–Se–Te chalcogenides, namely Se-substituted Ge–Sb–Te, have been developed as an alternative optical phase change material (PCM) with a high figure-of-merit. A need for the integration of such new PCMs onto a variety of photonic platforms has necessitated the development of fabrication processes compatible with diverse material compositions as well as substrates of varying material types, shapes, and sizes. This study explores the application of chemical solution deposition as a method capable of creating conformally coated layers and delves into the resulting modifications in the structural and optical properties of Ge–Sb–Se–Te PCMs. Specifically, we detail the solution-based deposition of Ge–Sb–Se–Te layers and present a comparative analysis with those deposited via thermal evaporation. We also discuss our ongoing endeavor to improve available choice of processing-material combinations and how to realize solution-derived high figure-of-merit optical PCM layers, which will enable a new era for the development of reconfigurable photonic devices.

Effect of Ultraviolet Radiation on Properties of Ge2Sb2Te5 Phase Change Films.

With the expanding utilization of space technology, the stability of electronic components' performance in radiation environments has garnered significant attention. In this study, we prepared Ge2Sb2Te5 phase change films and memory units on silicon substrates to explore the influence of ultraviolet (UV) radiation on their characteristics. The experimental findings revealed that UV irradiation at a power density of 450 mW/cm2 decreased the amorphous resistance and thermal stability of Ge2Sb2Te5 films, impeding their multistage storage performance. Nevertheless, the amorphous state could still undergo effective transformation into a crystalline state. Furthermore, UV irradiation triggered the photoelectric effect, narrowing the band gap and causing a redshift of the Raman peak in amorphous films. Remarkably, the surface properties of Ge2Sb2Te5 films remained unchanged under irradiation. The phase change memory device based on Ge2Sb2Te5 film retained its SET-RESET conversion capability at a pulse width of 100 ns post-UV irradiation, demonstrating resilience against UV radiation. This study offers the practical insights for the application of phase change memory in space radiation environments.

Confined Crystallization Polyether-Based Flexible Phase Change Film for Thermal Management.

Phase change materials (PCMs) possess the potential to regulate temperature by utilizing their thermal properties to absorb and release heat. Nevertheless, the application of PCMs in thermal management is constrained by issues such as liquid leakage and limited flexibility. In this study, we propose a novel approach to address these challenges by incorporating a pore structure within nanofibers to confine the crystallization of phase change molecules, thereby enhancing the flexibility of the composite material. Additionally, inspired by the adaptive mechanisms observed in plants, we have developed a form stable PCM based on polyether, which effectively mitigates the issue of liquid leakage at higher temperatures. Despite being a solid-liquid PCM at its core, this material exhibits molecular-scale flow and macroscopic shape stability as a result of intermolecular forces. The composite film material possesses remarkable flexibility, efficient thermal management capabilities, adjustable phase transition temperature, and the ability to undergo repeated processing and utilization. Consequently, it holds promising potential for applications in personal thermal energy management.

Flexible phase change film based on lignin-derived porous carbon/Eicosane for wearable thermal management and microwave absorption

A flexible phase-change film with thermal management and microwave absorption capabilities was developed for use in wearable devices. The film was created using a solution casting method based on a porous carbon-loaded eicosane (LP33/EI) material. LP33 served as the porous encapsulation medium, while Eicosane (EI) acted as the phase change component. The flexible substrate was a blend of polyvinyl alcohol (PVA) and bacterial cellulose nanocellulose (BC). The ultrathin film had a thickness of 0.262 mm, and LP33/EI-4 exhibited exceptional mechanical strength of 188 MPa. Testing revealed that the phase transition process had melting and crystallization enthalpies of 134.71 J/g and 126.11 J/g, respectively. The encapsulation structure effectively prevented any leakage during the phase transition process. Under simulated solar irradiation of 200 mW/cm2, LP33/EI-4 achieved a photothermal conversion efficiency (η) of 89.46 %. Additionally, the porous LP33 structure and high dielectric loss contributed to remarkable microwave absorption capabilities of −42 dB in the X-band and − 52 dB in the Ku-band. Overall, LP33/EI films demonstrated exceptional performance in thermal management, energy storage, and microwave absorption, making them an ideal choice for a variety of applications in wearable devices.

Dual-phase coexistence enables to alleviate resistance drift in phase-change films

The amorphous phase-change materials with spontaneous structural relaxation leads to the resistance drift with the time for phase-change neuron synaptic devices. Here, we modify the phase change properties of the conventional Ge2Sb2Te5 (GST) material by introducing an SnS phase. It is found that the resistance drift coefficient of SnS-doped GST was decreased from 0.06 to 0.01. It can be proposed that the origin originates from the precipitation of GST nanocrystals accompanied by the precipitation of SnS crystals compared to single-phase GST compound systems. We also found that the decrease in resistance drift can be attributed to the narrowed bandgap from 0.65 to 0.43 eV after SnS-doping. Thus, this study reveals the quantitative relationship between the resistance drift and the band gap and proposes a new idea for alleviating the resistance drift by composition optimization, which is of great significance for finding a promising phase change material.

Flexible phase change film with motion sensing and tactile recognition for wearable thermal management

Phase change materials (PCMs) have gained significant interest in personal thermal management technologies owing to high latent heat capacity and isothermal phase transitions. However, achieving simultaneous thermal and wearing comfort remains a formidable challenge due to their solid rigidity and liquid leakage. In this work, a polyetheramine-based conductive phase change film was developed by introducing ion transport network and tetradecanol as phase change components encapsulated within the skeleton network. The film possesses adjustable heat storage density (79.5–163.4 J/g) and exceptional flexibility at room temperature. On the basis of desirable thermal regulation ability and ideal wearability, the film was successfully applied in the personal thermal management field and effectively regulated the human body temperature. Moreover, the film realized human motion sensing and object tactile recognition in real time with construction of the inner ion transport channels. This successful exploration provides a promising and scalable route towards intelligent wearable thermal management.

Evidence for Ge2Sb2Te5 phase formation upon crystallization of Ge-doped Sb2Te3 phase change films

In this work, we investigated the phase transition characteristics of Ge-doped Sb2Te3 phase change films prepared by the magnetron sputtering method. During the crystallization process of Ge-doped Sb2Te3 films, we observed a metastable phase and identified its crystal structure as the face-centered cubic Ge2Sb2Te5, a previously uncharacterized phenomenon. The Te phase precipitated upon crystallization of Sb2Te3 films, while the Te phase disappeared and the Ge2Sb2Te5 phase appeared upon crystallization of Ge-doped Sb2Te3 films, resulting in the coexistence of Ge2Sb2Te5 and Sb2Te3 phases in the single-layer Ge-doped Sb2Te3 films. The appearance of the Ge2Sb2Te5 phase resulted from the formation of Ge–Te bonds due to the combination of the precipitated Te phase with the incorporated Ge. Furthermore, the formation of the Ge2Sb2Te5 phase was mainly responsible for the increased crystalline resistance and crystallization temperature of Sb2Te3 films. The surface roughness of Ge-doped Sb2Te3 films was significantly reduced, exhibiting good potential for improving the contact performance between the films and electrodes. Our findings contribute to enhancing the understanding of Ge-doped Sb2Te3 films and their role in phase change memory technology.

Multifunctional phase change film with high recyclability, adjustable thermal responsiveness, and intrinsic self-healing ability for thermal energy storage

Phase change materials (PCMs) present promising potential for guaranteeing safety in thermal management systems. However, most reported PCMs have a single application in energy storage for thermal management systems, which does not meet the growing demand for multi-functional materials. In this paper, the flexible material and hydrogen-bonding function are innovatively combined to design and prepare a novel multi-functional flexible phase change film (PPL). The 0.2PPL-2 film exhibits solid-solid phase change behavior with energy storage density of 131.8 J/g at the transition temperature of 42.1 °C, thermal cycling stability (500 cycles), wide-temperature range flexibility (0–60 °C) and self-healing property. Notably, the PPL film can be recycled up to 98.5% by intrinsic remodeling. Moreover, the PPL film can be tailored to the desired colors and configurations and can be cleverly assembled on several thermal management systems at ambient temperature through its flexibility combined with shape-memory properties. More interestingly, the transmittance of PPL will be altered when the ambient temperature changes (60 °C), conveying a clear thermal signal. Finally, the thermal energy storage performance of the PPL film is successfully tested by human thermotherapy and electronic device temperature control experiments. The proposed functional integration strategy provides innovative ideas to design PCMs for multifunctionality, and makes significant contributions in green chemistry, high-efficiency thermal management, and energy sustainability.

Research on Improved Crystallization Properties and Underlying Mechanism of the Sb2Te3 Phase-Change Thin Film by Inserting Sn15Sb85 Layers.

As a non-volatile semiconductor memory technology, phase-change memory has a wide range of application prospects as a result of the excellent comprehensive performance. In this paper, multilayer thin films based on Sb2Te3 material were designed and prepared by inserting the Sn15Sb85 layer. The thermal and electrical properties of superlattice-like Sb2Te3/Sn15Sb85 phase-change films can be adjusted by controlling the thickness ratio of Sb2Te3/Sn15Sb85. In comparison to the monolayer Sb2Te3 film, the multilayer layer Sb2Te3/Sn15Sb85 materials have a higher crystallization temperature, larger crystallization activation energy, and longer data lifetime, indicating the great improvement of thermal stability. The changes in the phase structure and vibrational modes of multilayer Sb2Te3/Sn15Sb85 films were characterized by X-ray diffraction and Raman spectroscopy, respectively. The presence of Sn15Sb85 layers restrains grain growth and refines the grain size. The multilayer Sb2Te3/Sn15Sb85 films exhibit better surface flatness, smaller surface potential undulation, and lower thickness variations than single-layer Sb2Te3. Phase-change memory cells based on the [Sb2Te3 (1 nm)/Sn15Sb85 (9 nm)]5 thin film has a lower threshold voltage (1.9 V) and threshold current (3.1 μA) compared to the Ge2Sb2Te5 film. Meanwhile, the electrical heating model of a phase-change memory cell based on a [Sb2Te3 (1 nm)/Sn15Sb85 (9 nm)]5 multilayer structure was established by multiphysics coupling analysis, proving the great improvement in heat transfer performance and efficiency. The experimental and theoretical studies confirm that the insertion of the Sn15Sb85 layer can significantly improve the crystallization properties of Sb2Te3 films, paving the way for optimizing the phase-change materials by regulating the microstructural parameters.

Multifunction integration within magnetic CNT-bridged MXene/CoNi based phase change materials

Developing advanced nanocomposite phase change materials (PCMs) integrating zero-energy thermal management, microwave absorption, photothermal therapy and electrical signal detection can promote the leapfrog development of flexible wearable electronic devices. For this goal, we propose a multidimensional collaborative strategy combining two-dimensional (2D) MXene nanosheets with metal-organic framework-derived one-dimensional (1D) carbon nanotubes (CNTs) and zero-dimensional (0D) metal nanoparticles. After encapsulating paraffin wax (PW) in three-dimensional (3D) networked multidimensional MXene/CoNi–C, the resulting composite PCMs exhibit excellent thermal energy storage capacity and long-term thermally reliable stability. Benefiting from the synergistically enhanced photothermal effects of CNTs, Co/Ni nanoparticles and MXene, PW@MXene/CoNi–C can capture photons efficiently and transfer phonons quickly, yielding an ultrahigh photothermal conversion and storage efficiency of 97.5%. Additionally, PW@MXene/CoNi–C composite PCMs exhibit high microwave absorption with a minimum reflection loss of −49.3 ​dB at 8.03 ​GHz in heat-related electronic application scenarios. More attractively, the corresponding flexible phase change film can simultaneously achieve thermal management and electromagnetic shielding of electronic devices, as well as photothermal therapy and electrical signal detection for individuals. This functional integration design provides an important reference for developing advanced flexible multifunctional wearable materials and devices.

Effect of humidification on antimony-based flexible phase change memory

Ambient humidity has an important impact on the performance of flexible electronic devices, and wearable electronic devices will inevitably involve a high humidity environment. To investigate the impact of humidification on flexible phase-change memory, we prepared Sb phase-change film and memory device unit with polyether ether ketone as substrate, and studied the effect of humidification on the properties of the film and device. The results show that the effective transition from an amorphous to a crystalline state can still be achieved by the film after soaking in water for 55 min, and the phase transition temperature increases with the increase of soaking time. Water molecules refine the film grains, resulting in increased crystalline resistance. Sb is a hydrophilic material, and its hydrophilicity decreases after crystallization. The reversible conversion of SET-RESET can be realized under different pulse widths even after the phase change memory device is soaked in water and bent many times. This study shows that antimony-based flexible phase change memory has certain deformation self-healing ability and moisture resistance, which provides a way to expand its application environment.

Design of CuS composite carbon-based Ni Al-LDH multifunctional phase change composite with electromagnetic shielding performance and heat storage capacity

CuS-based composites are widely used in the fields related to photothermal energy storage and electromagnetic shielding and are excellent candidates for composites with phase change materials. To meet the requirements of micro-integration and electromagnetic resistance of electronic products and optimize the thermal management of electronic products, it is necessary to prepare new flexible composite phase change materials. In this paper, through the design of MPC@Ni Al-LDH/CuS double-layer structure, two-step vacuum filtration method is used, and the highly conductive materials CuS and MPC are introduced into the manufacture of PCM films. With the help of Ni Al-LDH, flame retardancy is introduced. The electromagnetic wave absorption performance is enhanced, and the existence of nano-cellulose (CNF) makes the film have excellent mechanical properties. Ni Al-LDH/MPC and CuS substrates with stable and high mechanical properties are prepared by ultrasonic treatment. According to scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform-infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), differential scanning calorimetry (DSC) and thermogravimetry (TG) characterizations, PEG successfully entered the MPC/CuS skeleton by vacuum filtration, and flexible phase change composite bilayers (MLPC) were obtained. Due to the synergistic effect of structure and components, the obtained composite film has many different excellent functions. Specifically, when MPC@Ni Al-LDH is 15 wt%, the phase transition enthalpy, thermal conductivity, electromagnetic shielding, and electrical conductivity are 146.8 J/g, 1.07 W/m·K, 38.8 dB and 126.4 S/m, respectively. The 3600 s infrared temperature measurement results show that the sample has stable thermal properties. Due to the presence of CuS, when MPC@Ni Al-LDH is 5 wt%, its absorbance can be kept at 1.51 L/(g·cm), and its photothermal conversion efficiency can reach 90.6 %. The MPC/CuS structure in the composite film provides many heat transfer channels, which reduces the phonon scattering in the heat transfer process and significantly increases thermal conductivity. Therefore, this multifunctional flexible phase change film can be used in photothermal conversion devices and for thermal management of electronic equipment, and it has broad application prospects in wearable equipment design due to its excellent electromagnetic shielding ability and infrared thermal stealth ability.

Investigation of Cu-Sn-Sb Thin Film for Ultra-Speed and Phase High-Reliability Change Memory Applications

SnSb (SS), a vital phase-change thin film, has attracted attention due to its excellent phase-change properties, but the poor amorphous stability and crystalline speed of SS greatly limit its application in rapid phase-transition memories. Here, we propose a copper (Cu)-doped SS phase change films to achieve ultra-speed and high-reliability of SS. Resistance-temperature tests show Cu-Sn-Sb possesses ultra-low crystalline and amorphous resistivity, higher phase transition speed, and lower activation energy. X-ray diffraction measurements illustrate the introduction of Cu ions hinders the growth of grains and reduce grains size. Atomic force microscopy characterizes the surface morphology of as-deposited and annealed Cu-Sn-Sb films, and difference of root-mean-square roughness before and after annealing promote Cu-Sn-Sb film is more reliable to touch electrodes. In addition, the ultra-low resistivity and fast transition speed effectively reduce thermal loss in SET and RESET process. The results reveal that Cu-Sn-Sb is a promising material for ultra-rapid phase change and high-reliability storage applications.

Dynamic strain coupling driven by structural phase transition in mixed-dimensional 2H-MoS2/VO2 van der Waals heterointerfaces

Mixed-dimensional van der Waals (vdW) heterostructures, integrated two-dimensional (2D) atomic crystals with three-dimensional (3D) functional materials, offer a powerful means to manipulating physical properties and generating unprecedented functionalities. Understanding interfacial couplings at those hetero (homo)-interfaces is indispensable for exploring new optical and electronic devices. Herein, we investigated dynamically phase-transition-driven strain coupling across a vdW heterointerface through integrating 2D layered 2H-MoS2 nanoflakes onto 3D phase-change VO2 epitaxial thin films. The Raman peak positions of the in-plane and out-of-plane vibration modes E2g1 and A1g from the 2H-MoS2 nanoflakes show a phonon softening and reversible hysteresis loop as a function of temperature in this mixed-dimensional vdW 2H-MoS2/(1¯11)-VO2/(11¯02)-Al2O3 heterostructure, originating from the co-action of temperature-dependent anharmonicity in 2H-MoS2 and reversible structural phase transition (SPT)-induced in-plane tensile strain from the VO2 thin film. Accordingly, the integrated Raman scattering intensity of these two feature peaks of the 2H-MoS2 nanoflakes increased (decreased) as the temperature increased (decreased), exhibiting a hysteresis loop in the SPT and metal–insulator transition region of VO2. Additionally, the peak integrated intensity enhancement ratio of the E2g1 and A1g vibration modes was approximately 2.3 and 2.8, respectively. These results indicate that the dynamically SPT-driven in-plane tensile strain from the bottom VO2 layer interfacially couples with the adjacent 2H-MoS2 nanoflakes and results in a reduction in the electronic transition energy, leading to an enhancement in the Raman scattering intensity of 2H-MoS2. Our work holds promise for dynamic strain control of lattice dynamics and electron–phonon interaction of 2D materials for functional electronic and photoelectronic devices.

Scalable Sol–Gel Permeation Assembly of Phase Change Layered Film Toward Thermal Management and Light‐Thermal Driving Applications

AbstractPhase change materials (PCMs) are pivotal in thermal energy management and conversion applications owing to their exceptional thermal energy storage and release characteristics. However, persistent challenges such as poor thermal conductivity and leakage issues have impeded their widespread adoption. While existing approaches mitigate these challenges by constructing and incorporating 3D thermal conductive networks, they are constrained by discontinuous preparation methods and mold size limitations. Herein, a scalable sol–gel permeation assembly strategy is proposed to prepare phase change layered film by in situ filling polyethylene glycol (PEG) in aramid nanofibers (ANF)/graphene nanoplates (GNP) network. Befitting from the laminated network encapsulation effect of ANF and GNP, the phase change film demonstrates leak‐free and stable phase transition behavior, even after undergoing 500 heating/cooling cycles. Moreover, the resulting PEG/ANF/GNP layered film exhibits an impressive in‐plane thermal conductivity of 23.7 W mK−1 at GNP loading of 28.1 vol.%, rendering it suitable for thermal management applications in electronic devices. The phase change layered film possesses exceptional photo‐thermal conversion properties, maintaining temperatures exceeding 90 °C under a light power density of 200 mW cm−2. Capitalizing on the thermally induced flexibility of the phase transition film and its temperature‐dependent stiffness, its utility extended to developing a light‐thermal driving gripper.

Configurable dual-topological-interface-states induced reflection in hybrid multilayers consisting of a Ge2Sb2Te5 film

Active control of induced reflection is crucial for many potential applications ranging from slowing light to biosensing devices. However, most previous approaches require patterned nanostructures to achieve controllable induced reflection, which hinders their further applications due to complicated architectures. Herein, we propose a lithography-free multilayered structure to achieve the induced reflection through the coupling of dual-topological-interface-states. The multilayers consist of two one-dimensional (1D) photonic crystals (PCs) and an Ag film separated by a Spacer, topological edge state (TES) and topological Tamm state (TTS) can be excited simultaneously and their coupling induces the reflection window. The coupled-oscillator model is proposed to mimic the coupling between the TES and TTS, and the analytical results are in good agreement with finite element method (FEM). In addition, the TES-TTS induced reflection is robust to the variation of structural parameters. By integrating an ultra-thin phase-change film of Ge2Sb2Te5 (GST) into the multilayers, the induced reflection can be switched through the phase transition of the GST film. The multipole decomposition reveals that the vanished reflection window is arising from the disappearance of TTS associated with the toroidal dipole (TD) mode.

Multi-level phase-change behaviors of Ge2Sb2Te5/Sb7Se3 bilayer films and a design rule of multi-level phase-change films

Multi-level phase-change (MLPC) memory can not only further raise the storage density of high-density phase-change memory, but also have significant applications in neuromorphic computing. However, acquisitions of MLPC materials are very challenging. MLPC is only observed in a small number of phase-change materials and can’t be designed determinately because the mechanism of MLPC emergence has been understood incompletely. Here, we investigate phase-change behaviors of six Ge2Sb2Te5(x nm)/Sb7Se3 (60-x nm) bilayer films with x = 5, 10, 15, 20, 35, and 50. Three-level phase-change memory is observed for five bilayer films with x < 50, but not for one with x = 50, revealing the dependence of MLPC memory on the thickness ratio of two constituent layers composing bilayer films. A parallel resistance model is proposed to describe the measured sheet resistance of bilayer films and can be used to explain the thickness-ratio dependence of three-level phase-change memory very well. Subsequently, a design rule for MLPC memory films is given out unambiguously. Based on the parallel resistance model, MLPC memories are simulated for bilayer and trilayer films. Three-level memory indeed appears in bilayer films only when the design rule is met, confirming the validity of our design rule. Four-level memory is predicted in trilayer films as the design rule is obeyed.

A polyurethane solid–solid phase change material for flexible use in thermal management

Phase change materials (PCMs) have received great attention in thermal management of electronic devices due to their high energy storage density and no need for additional energy supply. Yet the leakage problem after phase change limits their application greatly. In this paper, the block copolymerization was used to prepare a novel solid–solid phase change material (SSPCM) with a melting enthalpy of 90.26 J/g, starting pyrolysis at a temperature of more than 300 °C, and its physicochemical and thermal properties remained basically unchanged after 100 heating/cooling cycles. Notably, this SSPCM has excellent shape stability and can be pressed into phase change film with flexibility, thermally induced self-healing capability and recyclability. Finally, we innovatively combined this SSPCM, copper foam (CF), and polyimide tape (PI) to obtain a composite phase change material (CPCM) with both high thermal conductivity (1.1994 W/m·K) and high electrical insulating properties. Thermal management experiment shows that this CPCM has good thermal management performance and can significantly reduce the temperature rise rate of the simulated CPU. The SSPCM prepared in this study shows great potential for application in thermal management of portable electronic devices and flexible wearable electronic devices.

Flexible and Thermally Conductive Phase-Change Films with a Two-Level Network for Dual-Mode Thermal Management of Batteries

Flexible and Thermally Conductive Phase-Change Films with a Two-Level Network for Dual-Mode Thermal Management of Batteries