Fundamentals, Algorithms, and Technologies of Occupancy Detection for Smart Buildings Using IoT Sensors.

Smart buildings use advanced technologies to automate building functions. One important function is occupancy detection using Internet of Things (IoT) sensors for smart buildings. Occupancy information is useful information to reduce energy consumption by automating building functions such as lighting, heating, ventilation, and air conditioning systems. The information is useful to improve indoor air quality by ensuring that ventilation systems are used only when and where they are needed. Additionally, it is useful to enhance building security by detecting unusual or unexpected occupancy levels and triggering appropriate responses, such as alarms or alerts. Occupancy information is useful for many other applications, such as emergency response, plug load energy management, point-of-interest identification, etc. However, the accuracy of occupancy detection is limited by factors such as real-time occupancy data, sensor placement, privacy concerns, and the presence of pets or objects that can interfere with sensor reading. With the rapid development of IoT sensor technologies and the increasing need for smart building solutions, there is a growing interest in occupancy detection techniques. There is a need to provide a comprehensive survey of these technologies. Although there are some exciting survey papers, they all have limited scopes with different focuses. Therefore, this paper provides a comprehensive overview of the current state-of-the-art occupancy detection methods (including both traditional algorithms and machine learning algorithms) and devices with their advantages and limitations. It surveys and compares fundamental technologies (such as sensors, algorithms, etc.) for smart buildings. Furthermore, the survey provides insights and discussions, which can help researchers, practitioners, and stakeholders develop more effective occupancy detection solutions for smart buildings.

Stearic Acid as an Atomic Layer Deposition Inhibitor: Spectroscopic Insights from AFM-IR.

Modern-day chip manufacturing requires precision in placing chip materials on complex and patterned structures. Area-selective atomic layer deposition (AS-ALD) is a self-aligned manufacturing technique with high precision and control, which offers cost effectiveness compared to the traditional patterning techniques. Self-assembled monolayers (SAMs) have been explored as an avenue for realizing AS-ALD, wherein surface-active sites are modified in a specific pattern via SAMs that are inert to metal deposition, enabling ALD nucleation on the substrate selectively. However, key limitations have limited the potential of AS-ALD as a patterning method. The choice of molecules for ALD blocking SAMs is sparse; furthermore, deficiency in the proper understanding of the SAM chemistry and its changes upon metal layer deposition further adds to the challenges. In this work, we have addressed the above challenges by using nanoscale infrared spectroscopy to investigate the potential of stearic acid (SA) as an ALD inhibiting SAM. We show that SA monolayers on Co and Cu substrates can inhibit ZnO ALD growth on par with other commonly used SAMs, which demonstrates its viability towards AS-ALD. We complement these measurements with AFM-IR, which is a surface-sensitive spatially resolved technique, to obtain spectral insights into the ALD-treated SAMs. The significant insight obtained from AFM-IR is that SA SAMs do not desorb or degrade with ALD, but rather undergo a change in substrate coordination modes, which can affect ALD growth on substrates.

Penetrating glassy carbon neural electrode arrays for brain-machine interfaces.

This paper presents a fabrication method for glassy carbon neural electrode arrays that combines 3D printing and chemical pyrolysis technology. The carbon electrodes have excellent biological compatibility and can be used in neural signal recording. A pretreated Si wafer is used as the substrate for 3D printing, and then, stereolithography 3D printing technology is employed to print photosensitive resin into a cone shape. Next, chemical pyrolysis is applied to convert the 3D prints into glassy carbon electrodes and modify the electrochemical performance of the carbon electrodes. Finally, the glassy carbon electrodes are packed with conductive wires and PDMS. The proposed fabrication method simplifies the manufacturing process of carbon materials, and electrodes can be fabricated without the need of deep reactive ion etching (DRIE). The height of the carbon electrodes is 1.5 mm, and the exposure area of the tips is 0.78 mm2, which is convenient for the implantation procedure. The specific capacitance of the glassy carbon arrays is higher than that of a platinum electrode (9.18 mF/cm2 vs 3.32 mF/cm2, respectively), and the impedance at 1 kHz is lower (7.1 kΩ vs 8.8 kΩ). The carbon electrodes were tested in vivo, and they showed excellent performance in neural signal recording. The signal-to-noise ratio of the carbon electrodes is 50.73 ± 6.11, which is higher than that of the Pt electrode (20.15 ± 5.32) under the same testing conditions. The proposed fabrication method of glassy carbon electrodes provides a novel approach to manufacture penetrating electrodes for nerve interfaces in biomedical engineering and microelectromechanical systems.

Flexible 3D carbon nanotubes cuff electrodes as a peripheral nerve interface.

The cuff electrode provides a stable interface with peripheral nerves, which has been widely used in basic research and clinical practice. Currently, the cuff electrodes are limited by the planar processing of microfabrication. This paper presents a novel cuff electrode using high-aspect ratio carbon nanotubes (CNTs) integrated on a flexible biocompatible parylene. The microfabrication process unites the high quality vertical CNTs grown at high temperature with the heat sensitive parylene substrate in a highly controllable manner. The fabricated cuff electrodes have been utilized for extracellular nerve stimulation in rats. The experimental results demonstrate the proposed CNT electrode has a better performance than Pt electrode in nerve stimulation. Moreover, the effect of electrode position and stimulation frequency is demonstrated in this paper. This preliminary data indicates that flexible 3D CNTs cuff electrode provides an excellent platform for functional electrical stimulation.

A novel fabrication method of carbon electrodes using 3D printing and chemical modification process.

Three-dimensional (3D) printing is an emerging technique in the field of biomedical engineering and electronics. This paper presents a novel biofabrication method of implantable carbon electrodes with several advantages including fast prototyping, patient-specific and miniaturization without expensive cleanroom. The method combines stereolithography in additive manufacturing and chemical modification processes to fabricate electrically conductive carbon electrodes. The stereolithography allows the structures to be 3D printed with very fine resolution and desired shapes. The resin is then chemically modified to carbon using pyrolysis to enhance electrochemical performance. The electrochemical characteristics of 3D printing carbon electrodes are assessed by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The specific capacitance of 3D printing carbon electrodes is much higher than the same sized platinum (Pt) electrode. In-vivo electromyography (EMG) recording, 3D printing carbon electrodes exhibit much higher signal-to-noise ratio (40.63 ± 7.73) than Pt electrodes (14.26 ± 6.83). The proposed biofabrication method is envisioned to enable 3D printing in many emerging applications in biomedical engineering and electronics.

Toward individually tunable compound eyes with transparent graphene electrode.

We present tunable compound eyes made of ionic liquid lenses, of which both curvatures (R 1 and R 2 in the lensmaker's equation) can be individually changed using electrowetting on dielectric (EWOD) and applied pressure. Flexible graphene is used as a transparent electrode and is integrated on a flexible polydimethylsiloxane (PDMS)/parylene hybrid substrate. Graphene electrodes allow a large lens aperture diameter of between 2.4 mm and 2.74 mm. Spherical aberration analysis is performed using COMSOL to investigate the optical property of the lens under applied voltage and pressure. The final lens system shows a resolution of 645.1 line pair per millimeter. A prototype of a tunable lens array is proposed for the application of a compound eye.

Ultrathin and Atomically Flat Transition-Metal Oxide: Promising Building Blocks for Metal-Insulator Electronics.

We present a new and viable template-assisted thermal synthesis method for preparing amorphous ultrathin transition-metal oxides (TMOs) such as TiO2 and Ta2O5, which are converted from crystalline two-dimensional (2D) transition-metal dichalcogenides (TMDs) down to a few atomic layers. X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and scanning transmission electron microscopy (STEM) were used to characterize the chemical composition and bonding, surface morphology, and atomic structure of these ultrathin amorphous materials to validate the effectiveness of our synthesis approach. Furthermore, we have fabricated metal-insulator-metal (MIM) diodes using the TiO2 and Ta2O5 as ultrathin insulating layers with low potential barrier heights. Our MIM diodes show a clear transition from direct tunneling to Fowler-Nordheim tunneling, which was not observed in previously reported MIM diodes with TiO2 or Ta2O5 as the insulating layer. We attribute the improved performance of our MIM diodes to the excellent flatness and low pinhole/defect densities in our TMO insulting layers converted from 2D TMDs, which enable the low-threshold and controllable electron tunneling transport. We envision that it is possible to use the ultrathin TMOs converted from 2D TMDs as the insulating layer of a wide variety of metal-insulator and field-effect electronic devices for various applications ranging from microwave mixing, parametric conversion, infrared photodetection, emissive energy harvesting, to ultrafast electronic switching.

3D carbon nanofiber microelectrode arrays fabricated by plasma-assisted pyrolysis to enhance sensitivity and stability of real-time dopamine detection.

In this paper, we have fabricated 3D carbon nanofiber microelectrode arrays (MEAs) with highly reproducible and rich chemical surface areas for fast scan cyclic voltammetry (FSCV). Carbon nanofibers are created from negative photoresist by a new process called dual O2 plasma-assisted pyrolysis. The proposed approach significantly improves film adhesion and increases surface reactivity. We showcase our sensor's compatibility with FSCV analysis by demonstrating highly sensitive and stable FSCV dopamine measurements on a prototype 4-channel array. We envision with proper surface fuctionalization the 3D carbon nanofiber MEA enable sensitive and reliable detection of multiple neurotransmitters simultaneously.

Mirror-backed Dark Alumina: A Nearly Perfect Absorber for Thermoelectronics and Thermophotovotaics.

We present here a broadband, wide-angle, and polarization-independent nearly perfect absorber consisting of mirror-backed nanoporous alumina. By electrochemically anodizing the disordered multicomponent aluminum and properly tailoring the thickness and air-filling fraction of nanoporous alumina, according to the Maxwell-Garnet mixture theory, a large-area dark alumina can be made with excellent photothermal properties and absorption larger than 93% over a wide wavelength range spanning from near-infrared to ultraviolet light, i.e. 250 nm-2500 nm. The measured absorption is orders of magnitude greater than other reported anodized porous alumina, typically semi-transparent at similar wavelengths. This simple yet effective approach, however, does not require any lithography, nano-mixture deposition, pre- and post-treatment. Here, we also envisage and theoretically investigate the practical use of proposed absorbers and/or photothermal converters in integrated thermoelectronic and/or thermophotovoltaic energy conversion devices, which make efficient use of the entire spectrum of ambient visible to near-infrared radiation.

Versatile Miniature Tunable Liquid Lenses Using Transparent Graphene Electrodes.

This paper presents, for the first time, versatile and low-cost miniature liquid lenses with graphene as electrodes. Tunable focal length is achieved by changing the droplet curvature using electrowetting on dielectric (EWOD). Ionic liquid and KCl solution are utilized as lens liquid on the top of a flexible Teflon-coated PDMS/parylene membrane. Transparent and flexible, graphene allows transmission of visible light as well as large deformation of the polymer membrane to achieve requirements for different lens designs and to increase the field of view without damaging of electrodes. The tunable range for the focal length is between 3 and 7 mm for a droplet with a volume of 3 µL. The visualization of bone marrow dendritic cells is demonstrated by the liquid lens system with a high resolution (456 lp/mm).

Chemical-sensitive graphene modulator with a memory effect for internet-of-things applications.

Modern internet of things (IoTs) and ubiquitous sensor networks could potentially take advantage of chemically sensitive nanomaterials and nanostructures. However, their heterogeneous integration with other electronic modules on a networked sensor node, such as silicon-based modulators and memories, is inherently challenging because of compatibility and integration issues. Here we report a novel paradigm for sensing modulators: a graphene field-effect transistor device that directly modulates a radio frequency (RF) electrical carrier signal when exposed to chemical agents, with a memory effect in its electrochemical history. We demonstrated the concept and implementation of this graphene-based sensing modulator through a frequency-modulation (FM) experiment conducted in a modulation cycle consisting of alternating phases of air exposure and ethanol or water treatment. In addition, we observed an analog memory effect in terms of the charge neutrality point of the graphene, V cnp, which strongly influences the FM results, and developed a calibration method using electrochemical gate-voltage pulse sequences. This graphene-based multifunctional device shows great potential for use in a simple, low-cost, and ultracompact nanomaterial-based nodal architecture to enable continuous, real-time event-based monitoring in pervasive healthcare IoTs, ubiquitous security systems, and other chemical/molecular/gas monitoring applications.

A flexible and implantable microelectrode arrays using high-temperature grown vertical carbon nanotubes and a biocompatible polymer substrate.

This paper presents a novel microelectrode arrays using high-temperature grown vertically aligned carbon nanotubes (CNTs) integrated on a flexible and biocompatible parylene substrate. A simple microfabrication process is proposed to unite the high quality vertical CNTs grown at high temperature with the heat sensitive parylene substrate in a highly controllable manner. Briefly, the CNTs electrode is encapsulated by two layers of parylene and the device is released using xenon difluoride (XeF2). The process is compatible with wafer-scale post complementary metal oxide semiconductor integration. Lower impedance and larger interfacial capacitance have been demonstrated using CNTs compared to a Pt electrode. The flexible CNT electrodes have been utilized for extracellular neuronal recording and stimulation in rats. The signal-to-noise ratio of the device is about 12.5. The threshold voltage for initiating action potential is about 0.5 V.

A sandwich substrate for ultrasensitive and label-free SERS spectroscopic detection of folic acid / methotrexate.

A highly sensitive surface enhanced Raman scattering (SERS) substrate with particle-film sandwich geometry has been developed for the label free detection of folic acid (FA) and methotrexate (MTX). In this sandwich structure, the bottom layer is composed of a copper foil decorated with silver nanoparticles synthesized by the galvanic displacement reaction, and top layer is constituted by silver nanoparticles. The FA and MTX molecules are sandwiched between the silver nanoparticles decorated copper film and the silver nanoparticles. The plasmonic coupling between the two layers of the sandwich structure greatly enhances the SERS spectra of FA and MTX. SERS activity of the substrate was studied and optimized by adjusting the time of galvanic displacement reaction. The SERS spectra of the FA and MTX showed the minimum detection concentration of 100 pM. The identification of methotrexate and folic acid analogs was also carried out by SERS spectra analysis.

High mobility WSe2 p- and n-type field-effect transistors contacted by highly doped graphene for low-resistance contacts.

We report the fabrication of both n-type and p-type WSe2 field-effect transistors with hexagonal boron nitride passivated channels and ionic-liquid (IL)-gated graphene contacts. Our transport measurements reveal intrinsic channel properties including a metal-insulator transition at a characteristic conductivity close to the quantum conductance e(2)/h, a high ON/OFF ratio of >10(7) at 170 K, and large electron and hole mobility of µ ≈ 200 cm(2) V(-1 )s(-1) at 160 K. Decreasing the temperature to 77 K increases mobility of electrons to ∼330 cm(2) V(-1) s(-1) and that of holes to ∼270 cm(2) V(-1) s(-1). We attribute our ability to observe the intrinsic, phonon-limited conduction in both the electron and hole channels to the drastic reduction of the Schottky barriers between the channel and the graphene contact electrodes using IL gating. We elucidate this process by studying a Schottky diode consisting of a single graphene/WSe2 Schottky junction. Our results indicate the possibility to utilize chemically or electrostatically highly doped graphene for versatile, flexible, and transparent low-resistance ohmic contacts to a wide range of quasi-2D semiconductors.

Examining the inflammatory response to nanopatterned polydimethylsiloxane using organotypic brain slice methods.

A long-term effect of chronically implanted neural electrodes is the formation of a glial scar made up of reactive astrocytes, microglia and the matrix proteins they generate. Studies have shown glial fibrillary acidic protein (GFAP) and cytokines interleukin-1beta (IL-1ß), tumor necrosis factor alpha (TNFα), and transforming growth factor beta 1 (TGFß1) are involved with the initial and modulation phases of reactive astrogliosis. In the present study, nanopatterning of polydimethylsiloxane (PDMS) was attempted as a method for reducing the inflammatory response of glial cells. A unique feature of this study is the use of in vitro brain slice cultures (organotypic cultures) in order to more accurately depict the native response. The aim of the study was to determine whether nanotopography could reduce inflammatory signals typically resultant from neural electrode implantation. Specifically, observation of cell alignment and surveillance of GFAP, IL-1ß, TNFα, and TGFß1 gene expression around the PDMS pins was performed. Results of this study confirm nanopatterning not only influences cell morphology, but some of the molecular signals as well. These results collectively indicate nanopatterning improves the biocompatibility of PDMS by reducing inflammatory markers such as GFAP, IL-1ß, TGFß1 and TNFα compared to the non-patterned PDMS pins.

Improved carrier mobility in few-layer MoS2 field-effect transistors with ionic-liquid gating.

We report the fabrication of ionic liquid (IL)-gated field-effect transistors (FETs) consisting of bilayer and few-layer MoS2. Our transport measurements indicate that the electron mobility µ ≈ 60 cm(2) V(-1) s(-1) at 250 K in IL-gated devices exceeds significantly that of comparable back-gated devices. IL-FETs display a mobility increase from ≈ 100 cm(2) V(-1) s(-1) at 180 K to ≈ 220 cm(2) V(-1) s(-1) at 77 K in good agreement with the true channel mobility determined from four-terminal measurements, ambipolar behavior with a high ON/OFF ratio >10(7) (10(4)) for electrons (holes), and a near ideal subthreshold swing of ≈ 50 mV/dec at 250 K. We attribute the observed performance enhancement, specifically the increased carrier mobility that is limited by phonons, to the reduction of the Schottky barrier at the source and drain electrode by band bending caused by the ultrathin IL dielectric layer.

Electrowetting on dielectric experiments using graphene.

We report electrowetting on dielectric (EWOD) experiments using graphene; a transparent, flexible and stretchable nanomaterial. Graphene sheets were synthesized by chemical vapor deposition, and transferred to various substrates (including glass slides and PET films). Reversible contact angle changes were observed on the Teflon-coated graphene electrode with both AC and DC voltages. Nyquist plots of the EWOD reveal that the graphene electrode has higher capacitive impedance than gold electrodes under otherwise identical conditions, suggesting a lower density of pin-holes and defects in the Teflon/graphene electrode than in the Teflon/gold electrode. Furthermore, we have observed reduced electrolysis of the electrolyte and smaller leakage current in the dielectric layer (Teflon) on graphene electrodes than on Au electrodes at the same Teflon thickness and applied voltage. We expect that the improved EWOD properties using graphene as an electrode material will open the door to various applications, including flexible displays and droplet manipulation in three-dimensional microfluidics.

Room-temperature high on/off ratio in suspended graphene nanoribbon field-effect transistors.

We have fabricated suspended few-layer (1-3 layers) graphene nanoribbon field-effect transistors from unzipped multi-wall carbon nanotubes. Electrical transport measurements show that current annealing effectively removes the impurities on the suspended graphene nanoribbons, uncovering the intrinsic ambipolar transfer characteristic of graphene. Further increasing the annealing current creates a narrow constriction in the ribbon, leading to the formation of a large bandgap and subsequent high on/off ratio (which can exceed 10(4)). Such fabricated devices are thermally and mechanically stable: repeated thermal cycling has little effect on their electrical properties. This work shows for the first time that ambipolar field-effect characteristics and high on/off ratios at room temperature can be achieved in relatively wide graphene nanoribbons (15-50 nm) by controlled current annealing.

Mesoporous silicon particles as a multistage delivery system for imaging and therapeutic applications.

Many nanosized particulate systems are being developed as intravascular carriers to increase the levels of therapeutic agents delivered to targets, with the fewest side effects. The surface of these carriers is often functionalized with biological recognition molecules for specific, targeted delivery. However, there are a series of biological barriers in the body that prevent these carriers from localizing at their targets at sufficiently high therapeutic concentrations. Here we show a multistage delivery system that can carry, release over time and deliver two types of nanoparticles into primary endothelial cells. The multistage delivery system is based on biodegradable and biocompatible mesoporous silicon particles that have well-controlled shapes, sizes and pores. The use of this system is envisioned to open new avenues for avoiding biological barriers and delivering more than one therapeutic agent to the target at a time, in a time-controlled fashion.

Biomedical nanotechnology for cancer.

Nanotechnology may hold the key to controlling many devastating diseases. In the fight against the pain, suffering, and death due to cancer, nanotechnology will allow earlier diagnosis and even prevention of malignancy at premalignant stages, in addition to providing multimodality treatment not possible with current conventional techniques. This review discusses nanotechnology already used in diagnostic and therapeutic applications for cancer. Also addressed are theoretic and evolving uses of nanotechnology, including multifunctional nanoparticles for imaging and therapy, nanochannel implants for controlled release of drugs, nanoscale devices for evaluation of proteomics and genomics, and diagnostic techniques that take advantage of physical changes in diseased tissue.