Annealing Step Research Articles

Improved Performance of Silicon Anodes Using Copper Nanoparticles as Additive

Abstract Nanoscale copper has been successfully integrated into a silicon-based anode via a cost-effective, one-step process. The additive was found to improve the overall electrical conductivity and charge/discharge cycling performance of the anode. Analysis of the new material shows that copper particles are homogeneously interspersed into the silicon active layer. The formation of Cu3Si during the annealing step of the fabrication process was also confirmed using X-ray diffraction and is thought to contribute to the structural stability of the anode during cycling. Despite the inclusion of only small quantities of the additive (approximately 3%), anodes with the added copper show significantly higher initial discharge capacity values (957 mAg−1) compared to anodes without copper (309 mAg−1), and they continue to outperform the latter after 100 charge/discharge cycles. Results also show a significant decrease in the resistance of anodes with the additive, a contributing factor in the improvement of the electrochemical performance.

Al2O3/ZnO composite-based sensors for battery safety applications: An experimental and theoretical investigation

Lithium-ion batteries are vital in one of the key nanotechnologies required for the transition to a carbon-free society. As such, they are under constant investigation to improve their performance in terms of energy and power densities. At the same time, safety monitoring is crucial, as defects in the battery cell can lead to serious safety risks such as fires and explosions as a result of the enormous heat generated in the electrolyte, causing the release of toxic and flammable gases in the so-called thermal runaway. Therefore, early and rapid detection of the gases that form before thermal runaway is of particular interest. To this end, solid-state sensors based on new heterostructured materials have gained interest owing to their high stability and versatility when used in the harsh battery environment. In this work, heterostructures based on semiconductor oxides are employed as sensors for typical components of battery electrolytes and their decomposition products. The sensors showed a significant response to vapors produced by battery solvents or degassing products, making them perfect candidates for the development of successful new prototypes for safety monitoring. Here, we have used a simple and versatile method to fabricate the Al2O3/ZnO heterostructure, consisting of atomic layer deposition (ALD) and thermal annealing steps. These Al2O3/ZnO heterostructures have shown a response to the vapours of 1,3-dioxolane (DOL, C3H6O2), 1,2-dimethoxyethane (DME, C4H10O2), LiPF6, ethylene carbonate (EC) and dimethyl carbonate (DMC), which are typically used as components of the electrolytes in LIBs. The sensors showed a significant response to vapors produced by battery solvents or degassing products, significantly increasing the chances of developing new successful prototypes for safety monitoring. Density functional theory (DFT) calculations were employed to systematically compare the surface reactivity of the α-Al2O3(0001) and the ZnO101̅0 facets, as well as the Al2O3/ZnO101̅0 interface, towards C3H6O2, C4H10O2, nitrogen dioxide (NO2) and phosphorous pentafluoride (PF5), in addition to H2O to assess the impact of relative humidity on the performance of the gas detector. The scanning tunnelling microscopy (STM) images and molecular binding energies compare well with our experiments. The energies of molecular adsorption at the heterostructure suggest that humidity will not affect the detection of the volatile organic compounds. The results presented here show that the potential to detect vapors of the components used in the electrolytes of LIBs, combined with the size control provided by the synthesis method, makes these heterostructures extremely attractive in devices to monitor battery safety.

Stable Room Temperature Nitrenes Created by Photolysis of Crystalline 4-Azido-2,3,5,6-tetrafluorobenzoic Acid

The structure, spectroscopy, and photochemistry of 4-azidobenzoic acid (4ABC) and its perfluorinated analog 4-azido-2,3,5,6-tetrafluorobenzoic acid (4F4ABC) are characterized in frozen glasses and crystals. Photolysis of the parent azides leads to the production of nitrenes and other spin species that are probed by electron paramagnetic resonance and optical spectroscopy. Shifts in the absorption spectra for both the parent azides and the nitrenes were well reproduced using density functional calculations. Photolysis generates ∼10× higher yield of the triplet nitrene relative to the quintet and radical side-products in 4F4ABC, while the opposite ratio is observed in 4ABC. An annealing step further suppressed the side-products in 4F4ABC, creating a solid where nitrenes were the dominant spin species. The nitrene in the 4F4ABC crystal has a 1/e lifetime of 20 days at room temperature in open air. This stability makes it possible to photopattern nitrene centers into a single crystal and characterize their photoluminescence. Multiple observations suggest that the remarkable stability in the 4F4ABC crystal is a consequence of crystal packing that traps N2 molecules adjacent to the nitrene. The ability to create stable, solid-state nitrene samples may provide a route to organic high-spin materials with potential applications in spintronics and quantum information science.

Competitive actions of MnSi in the epitaxial growth of Mn5Si3 thin films on Si(111)

Some magnetically ordered phases of the ${\mathrm{Mn}}_{5}{\mathrm{Si}}_{3}$ crystal are proving to be prototypes for the study of the new fundamental spin physics related to the spontaneous breaking of the time-reversal symmetry despite a zero net magnetization. Here, we report on a route to grow epitaxial ${\mathrm{Mn}}_{5}{\mathrm{Si}}_{3}$ thin films on Si(111). To this end, we use Mn and Si codeposition in a molecular beam epitaxy system and carefully tune the deposition rates, the growth temperature, and the annealing temperature. We assessed the silicide phase-formation and morphology using reflection high-energy electron diffraction, x-ray diffraction, high-resolution transmission electron microscopy (HRTEM) and atomic force microscopy. Layers containing only ${\mathrm{Mn}}_{5}{\mathrm{Si}}_{3}$ could be stabilized under very restrictive conditions, by tuning the Mn/Si flux ratio to match the compound stoichiometry and adjusting the substrate temperature during growth to 443 K. HRTEM imaging revealed the existence of an interfacial amorphous layer of few nanometers thickness. Annealing the heterostructure up to 573 K led to the formation of MnSi at the vicinity of the ${\mathrm{Mn}}_{5}{\mathrm{Si}}_{3}$/Si(111) interface, which significantly reduced the nucleation barrier of ${\mathrm{Mn}}_{5}{\mathrm{Si}}_{3}$. High-quality crystalline ${\mathrm{Mn}}_{5}{\mathrm{Si}}_{3}$ thin films were then formed with the following epitaxial relationships: ${\mathrm{Mn}}_{5}{\mathrm{Si}}_{3}$(0001)$[01\overline{1}0]//\mathrm{MnSi}(111)[\overline{2}11]//\mathrm{Si}(111)[1\overline{1}0]$. Our experiments showed that the formation of MnSi is enhanced at a growth temperature above 473 K or for a longer annealing step, while the crystalline quality of the ${\mathrm{Mn}}_{5}{\mathrm{Si}}_{3}$ overlayer is correspondingly degraded leading to textured thin films. The growth pathways and structural properties of the manganese silicides can be rationalized in terms of reactions maximizing the free-energy lowering rate. Moreover, we found that the magnetic and the magnetotransport properties can be used as an efficient tool to track both ${\mathrm{Mn}}_{5}{\mathrm{Si}}_{3}$ crystallinity and proportion in the deposited layers.

Prediction of Unwanted Crystallization of Freeze-Dried Protein Formulations Using α-Relaxation Measurements.

There is a lack of methods to predict the isothermal crystallization behavior of amorphous freeze-dried formulations stored below the glass transition temperature. This study applies isothermal microcalorimetry to predict long-term crystallization during product storage time. The relaxation curve of a fresh sample recorded within 12 h after lyophilization is correlated with the long-term crystallization time at the same temperature. Storage conditions of 25 °C and 40 °C are examined and five model formulations containing either sucrose or trehalose with different concentrations of an IgG1 antibody are investigated. The amorphous formulations were created by different freeze-drying processes only differing in their freezing step (random nucleation; additional annealing step of 1.5 h and 3 h, controlled nucleation; quench cooling). Samples that crystallized during the study time of 12 months showed a promising correlation between their relaxation time and crystallization behavior upon storage. Furthermore, the study shows that polysorbate 20 strongly accelerates crystallization of sucrose and that the freezing step itself has a strong impact on the relaxation phenomena that is not levelled out by primary and secondary drying.

Development of the differential detection reverse transcription loop-mediated isothermal amplification method for Barley yellow mosaic virus or Japanese soil-borne wheat mosaic virus from barley.

A differential detection reverse transcription loop-mediated isothermal amplification (DD-RT-LAMP) method was developed to detect either Barley yellow mosaic virus (BaYMV) or Japanese soil-borne wheat mosaic virus (JSBWMV) simultaneously. Both primer sets, which recognized either BaYMV or JSBWMV genomic RNA, amplified DNA more efficiently at 65°C using an isothermal DNA amplification and fluorescence detection device. Furthermore, these primer sets showed unique annealing curves. The peak annealing temperatures of BaYMV and JSBWMV amplification products using specific primer sets were 86.9°C-87.7°C and 84.5°C-85.0°C, respectively, and were clearly distinguishable during an annealing step following the isothermal amplification, monitored using a fluorescence detection device. In the field samples of barley (Hordeum vulgare L.) tested, BaYMV or JSBWMV were detected by DD-RT-LAMP, and the detection results of DD-RT-LAMP were correspondent with the results of reverse transcription-PCR.

New blue pigments based on Co2+ and La3+ doped hibonite for NIR-reflective coatings

New blue pigments based on Ca1-xLaxAl12-xCoxO19 (x = 0–0.5) were obtained by the combustion method, avoiding the expensive annealing step. The obtained pigments have a specific surface area between 3 and 5 m2/g. The crystallite size of Ca1-xLaxAl12-xCoxO19 pigments decreases from 44 to 26 nm, as the substitution degree, x, increases from 0 to 0.5 apfu. Despite the low Co2+ content (<4% mass), the pigments show intense blue shades and high total solar reflectance. CIE L∗/a∗/b∗ parameters show that, with the increase of chromophore content from 0.1 apfu (73.3/-2.6/-34.1) to 0.5 apfu (60.5/2.6/-47.0) the blue color of the pigments intensifies, whilst the total solar reflectance decreases from 70.7% (x = 0.1) to 59.6% (x = 0.5). The tests performed confirmed the possibility of using Ca1-xLaxAl12-xCoxO19 pigments in making cool, NIR-reflective coatings.

Structure-Engineered Core–Shell Ni–Co–O/NiCo-LDH Nanospheres as High-Performance Supercapacitor Electrodes

The development of a novel electrode material for energy storage devices is a grand challenge. Here, through a rational design of the structure, the electrochemical performance of the prepared sample could be improved while enhancing the conductivity and the synergistic effect of its components. Herein, we constructed a core–shell composite named Ni–Co–O/NiCo-LDH as the electrode material by a self-template method, which comprised hydrothermal and annealing steps. The as-prepared material exhibited a Chinese chestnut-like structure, and the core–shell structure was based on nanoneedles. The pseudocapacitance characteristics of the Ni–Co–O/NiCo-LDH electrode were significantly improved due to the good electrical conductivity of the core material and the unique core–shell structure, which led to a high electrochemical performance, reaching a high specific capacitance of 1434 F g−1 at the current density of 1 A g−1. When assembled in a device with activated carbon (AC) as the negative electrode, the supercapacitor showed an energy density of 26 Wh kg−1 at a power density of 807 W kg−1. Simultaneously, the device showed an excellent cycle stability, with 95% capacity retention after 3600 cycles at a current density of 6 A g−1, which could largely widen the application of the supercapacitor.

A Two‐in‐One Annealing Enables Dopant Free Block Copolymer Based Organic Solar Cells with over 16% Efficiency

Comprehensive SummaryThe organic solar cells (OSCs) based on block copolymer systems bear the hope of achieving the optimal balance of power conversion efficiency (PCE) and stability, but the key index, PCE of this type devices is still low. To improve the efficiency, regulating the thin‐film morphology is always the core engineering, which is usually achieved via two aspects: precursor optimization and post treatments. Herein, we extend our previous success in post treatments (two step annealing) to a novel two‐in‐one annealing tactic, which realizes limited phase separation and well‐connected domain distribution. As a result, the optimal PCE as high as 16.08%, representing the cutting‐edge level of block copolymer based OSCs (notably dopant free). Furthermore, a comprehensive study on all kinds of annealing methods is carried out, including TA, SVA, SVA+TA, TA+SVA and SVTA (the best one), and an in‐depth understanding is demonstrated, with the help of different characterizations.

Nanodiodes on a Digestible Substrate

Biodegradable and edible electronics will need electronic components for signal modulation and wireless communication; hence, non-linear and high frequency components will be required. Here, a method to fabricate nanodiodes on isomalt (a sugar substitute) substrates is reported. Coplanar electrodes of Al and Au with nanogap separation were fabricated on top of isomalt through design of an adhesion lithography process specifically to accommodate the low melting point and high solubility of the substrate. Lateral diodes with rectification ratios of 103 were created by depositing indium gallium zinc oxide (IGZO) using a target with an atomic ratio of In2O3:Ga2O3:ZnO (1:1:1) on top of the electrodes without an annealing step.

High Crystallinity Ge Growth on Si (111) and Si (110) by Using Reduced Pressure Chemical Vapor Deposition

A method for high quality epitaxial growth of Ge on Si (111) and Si (110) is investigated by reduced pressure chemical vapor deposition. Two step Ge epitaxy (low temperature Ge seed and high temperature main Ge growth) with several cycles of annealing by interrupting the Ge growth (cyclic annealing) is performed. In the case of Ge seed layer growth below 350 °C for (111) and 400 °C for (110) orientation, huge surface roughening due to too high dislocation density is observed after the following annealing step. For both crystal orientations, a high crystallinity Ge seed layer is realized by combination of 450 °C growth with 800 °C annealing. Once the high-quality Ge seed layer is deposited, high crystal quality Ge can be grown at 600 °C on the seed layer for both crystal orientations. For the 5 μm thick Ge layer deposited with the cyclic annealing process at 800 °C, a Si diffusion length of ∼400 nm from the interface, RMS roughness below 0.5 nm and threading dislocation density of 5 × 106 cm−2 are achieved for both (111) and (110) substrates.

POM@ZIF Derived Mixed Metal Oxide Catalysts for Sustained Electrocatalytic Oxygen Evolution.

The design of efficient and stable oxygen evolution reaction (OER) catalysts based on noble-metal-free materials is crucial for energy conversion and storage. In this work, it was demonstrated how polyoxometalate (POM)-doped ZIF-67 can be converted into a stable oxygen evolution electrocatalyst by chemical etching, cation exchange, and thermal annealing steps. Characterization by X-ray photoelectron spectroscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy and Raman spectroscopy indicate that POM-doped ZIF-67 derived carbon-supported metal oxides were synthesized. The resulting composite shows structural and compositional advantages which lead to low overpotential (306 mV at j=10 mA ⋅ cm-2 ) and long-term stability under harsh OER conditions (1.0 M aqueous KOH).

Hybrid potentiodynamic/potentiostatic electrodeposition of thin and compact tin dioxide on indium tin oxide electrodes

Electrodeposition of conformal and compact SnO2 films on transparent conductive oxides (TCOs) has been hardly achieved thus limiting its application in fully solid solar cells such as those based in perovskite absorbers. Here are presented high-quality n-type semiconducting tin (VI) oxide (SnO2) thin films, successfully grown using a hybrid potentiodynamic/potentiostatic approach on both ITO and FTO coated glass substrates after a detailed optimization that included both annealing steps between eletrodepositions. A solution chemistry study together with a spectrophotometric analysis was useful to determine the one-hour time window of stability for the chosen electrolyte as source of tin. Formation mechanisms based in thermodynamic data and accumulated mass measurements using an electrochemical quartz crystal microbalance (EQCM) are discussed. From the EQCM study the growth rate of films was also estimated in good agreement with high resolution transmission electron microscopy (HR-TEM) analysis. Field emission scanning electron microscopy (FE-SEM) images and X-ray diffraction (XRD) data revealed that substrates are well-covered, crystalline, conformal and free of defects (e.g. without pinholes). The absence of these defects was also well supported by cyclic voltammetry measurements using the ferricyanide/ferrocyanide redox couple. XPS also confirmed the presence of Sn4+ in optimized films. From the optical properties, after carefully eliminating the influence of oscillations due to interference, a direct bandgap energy at 3.60 eV can be deduced. Another indirect bandgap energy at 3.30 eV can also be possible. The hybrid potentiodynamic/potentiostatic protocol to prepare SnO2 paves a way to prepare compact, transparent and well covering films suitable as electron transporting layer (ETL) for applications in both photoelectrochemical and solid-state solar cells.

Modeling of Masked Droplet Deposition for Site-Controlled Ga Droplets.

Site-controlled Ga droplets on AlGaAs substrates are fabricated using area-selective deposition of Ga through apertures in a mask during molecular beam epitaxy (MBE). The Ga droplets can be crystallized into GaAs quantum dots using a crystallization step under As flux. In order to model the complex process, including the masked deposition of the droplets and a reduction of their number during a thermal annealing step, a multiscale kinetic Monte Carlo (mkMC) simulation of self-assembled Ga droplet formation on AlGaAs is expanded for area-selective deposition. The simulation has only two free model parameters: the activation energy for surface diffusion and the activation energy for thermal escape of adatoms from a droplet. Simulated droplet numbers within the opening of the aperture agree quantitatively with the experimental results down to the perfect site-control, with one droplet per aperture. However, the model parameters are different compared to those of the self-assembled droplet growth. We attribute this to the presence of the mask in close proximity to the surface, which modifies the local process temperature and the As background. This approach also explains the dependence of the model parameters on the size of the aperture.

Thermal Recovery of the Electrochemically Degraded LiCoO2/Li7La3Zr2O12:Al,Ta Interface in an All-Solid-State Lithium Battery.

All-solid-state lithium batteries are promising candidates for next-generation energy storage systems. Their performance critically depends on the capacity and cycling stability of the cathodic layer. Cells with a garnet Li7La3Zr2O12 (LLZO) electrolyte can show high areal storage capacity. However, they commonly suffer from performance degradation during cycling. For fully inorganic cells based on LiCoO2 (LCO) as cathode active material and LLZO, the electrochemically induced interface amorphization has been identified as an origin of the performance degradation. This study shows that the amorphized interface can be recrystallized by thermal recovery (annealing) with nearly full restoration of the cell performance. The structural and chemical changes at the LCO/LLZO heterointerface associated with degradation and recovery were analyzed in detail and justified by thermodynamic modeling. Based on this comprehensive understanding, this work demonstrates a facile way to recover more than 80% of the initial storage capacity through a thermal recovery (annealing) step. The thermal recovery can be potentially used for cost-efficient recycling of ceramic all-solid-state batteries.

Ni-Pd-Incorporated Fe3O4 Yolk-Shelled Nanospheres as Efficient Magnetically Recyclable Catalysts for Reduction of N-Containing Unsaturated Compounds

The use of metal-based heterogeneous catalysts for the degradation of N-containing organic dyes has attracted much attention due to their excellent treatment efficiency and capability. Here, we report the synthesis of heterometals (Ni and Pd)-incorporated Fe3O4 (Ni-Pd/Fe3O4) yolk-shelled nanospheres for the catalytic reduction of N-containing organic dyes using a facile combination of solvothermal treatment and high-temperature annealing steps. Benefiting from the magnetic properties and the yolk-shelled structure of the Fe3O4 support, as well as the uniformly dispersed active heterometals incorporated in the shell and yolk of spherical Fe3O4 nanoparticles, the as-prepared Ni-Pd/Fe3O4 composite shows excellent recyclability and enhanced catalytic activity for three N-containing organic dyes (e.g., 4-nitrophenol, Congo red, and methyl orange) compared with its mono metal counterparts (e.g., Ni/Fe3O4 and Pd/Fe3O4). In the 4-nitrophenol reduction reaction, the catalytic activity of Ni-Pd/Fe3O4 was superior to many Fe3O4-supported nanocatalysts reported within the last five years. This work provides an effective strategy to boost the activity of iron oxide-based catalytic materials via dual or even multiple heterometallic incorporation strategy and sheds new light on environmental catalysis.

Surface characterization of alkane viral anchoring films prepared by titanate-assisted organosilanization

Studies of virus adsorption on surfaces with optimized properties have attracted a lot of interest, mainly due to the influence of the surface in the retention, orientation and stability of the viral capsids. Besides, viruses in whole or in parts can be used as cages or vectors in different areas, such as biomedicine and materials science. A key requirement for virus nanocage application is their physical properties, i.e. their mechanical response and the distribution of surface charge, which determine virus-substrate interactions and stability. In the present work we show two examples of viruses exhibiting strong surface interactions on homogeneous hydrophobic surfaces. The surfaces were prepared by titanate assisted organosilanization, a sol-gel spin coating process, followed by a mild annealing step. We show by surface and interface spectroscopies that the process allows trapping triethoxy-octylsilane (OCTS) molecules, exhibiting a hydrophobic alkane rich surface finishing. Furthermore, the surfaces remain flat and behave as more efficient sorptive surfaces for virus particles than mica or graphite (HOPG). Also, we determine by atomic force microscopy (AFM) the mechanical properties of two types of viruses (human adenovirus and reovirus) and compare the results obtained on the OCTS functionalized surfaces with those obtained on mica and HOPG. Finally, the TIPT+OCTS surfaces were validated as platforms for the morphological and mechanical characterization of virus particles by using adenovirus as initial model and using HOPG and mica as standard control surfaces. Then, the same characteristics were determined on reovirus using TIPT+OCTS and HOPG, as an original contribution to the catalogue of physical properties of viral particles.

SnO2-Based Ultra-Flexible Humidity/Respiratory Sensor for Analysis of Human Breath.

Developing ultraflexible sensors using metal oxides is challenging due to the high-temperature annealing step in the fabrication process. Here, we demonstrate the ultraflexible relative humidity (RH) sensor on food plastic wrap by using 808 nm near-infrared (NIR) laser annealing for 1 min at a low temperature (26.2-40.8 °C). The wettability of plastic wraps coated with sol-gel solution is modulated to obtain uniform films. The surface morphology, local temperature, and electrical properties of the SnO2 resistor under NIR laser irradiation with a power of 16, 33, and 84 W/cm2 are investigated. The optimal device can detect wide-range RH from 15% to 70% with small incremental changes (0.1-2.2%). X-ray photoelectron spectroscopy reveals the relation between the surface binding condition and sensing response. Finally, the proposed sensor is attached onto the face mask to analyze the real-time human breath pattern in slow, normal, and fast modes, showing potential in wearable electronics or respiration monitoring.

Direct fabrication of arrays of Cu(In,Ga)Se2 micro solar cells by sputtering for micro-concentrator photovoltaics

Micro-concentrator photovoltaics combines efficiency boosting light concentration with low electrical losses due to thermally cool sub-millimeter sized solar cells. Thin-film Cu(In,Ga)Se2absorber layers do not suffer from edge recombination enabling miniaturization to the micrometer size, which allows for considerable material saving. Cu(In,Ga)Se2micro solar cells have achieved excellent efficiencies under concentrated light, when fabricated by materially-wasteful lithography processes. However, for commercial consideration, material-efficient synthesis approaches are required. In this work, we demonstrate a novel approach to produce arrays of Cu(In,Ga)Se2micro absorber layers through a two-step process, where a Cu-In-Ga precursor layer is sputtered onto a photolithographically structured resist, followed by lift-off and selenization. Our investigation shows a detrimental contamination of the Cu-In-Ga micro-dots by the photoresist. Therefore, we introduce an additional annealing step in inert-gas atmosphere prior to the selenization step, which leads to the formation of electroactive Cu(In,Ga)Se2 micro absorbers. We report the synthesis and characterization of working micro solar cells with an efficiency of 1.2% under 1 Sun. This proof of principle opens up a new material-efficient synthesis route for the direct fabrication of arrays of micro solar cells and puts forward the potential to achieve higher power conversion efficiencies upon further process optimization.

Two-photon polymerization based reusable master template to fabricate polymer microneedles for drug delivery

Microneedle patches have been widely used in a minimally invasive manner for various drug delivery applications. However, for developing these microneedle patches, master molds are required, which are generally made of metal and are very expensive. Two-photon polymerization (2PP) technique can be used for fabricating microneedles more precisely and at a much lower cost. This study reports a novel strategy for developing microneedle master templates using the 2PP method. The main advantage of this technique is that there is no requirement for post-processing after laser writing, and that for the fabrication of polydimethylsiloxane (PDMS) molds, harsh chemical treatments such as silanization are not required. This is a one-step process for manufacturing of microneedle templates which allows easy replication of negative PDMS molds. This is done by adding resin to the master-template and annealing at a specific temperature, thereby making the PDMS peel-off easy and allowing re-use of the master template multiple times. Using this PDMS mold, two types of polyvinyl alcohol (PVA)-rhodamine (RD) microneedle patches were developed, namely, dissolving (D-PVA) and hydrogel (H-PVA) patches and were characterized using suitable techniques. This technique is affordable, efficient and does not require post-processing for development of microneedle templates required for drug delivery applications.•Two photon polymerization can be used for cost-effective fabrication of polymer microneedles for transdermal drug delivery.•Post-processing or surface-modification procedures are not required for these master templates.•Using a simple annealing step, the master template becomes reusable and robust for peeling off polymers like PDMS.