Research

(1) Spin Based Computer Devices, Sensors, and Energy Conversion Systems

Lead and Contact person: Pawan Tyagi

Co-PI Hongmei Dang, Kate Klein

(1) Spin Based Computer Devices, Sensors, and Energy Conversion Systems: Utilize quantum properties of single molecular magnets and a wide range of other molecules like DNA, porphyrin, organometallics, etc. for producing spin-based random-access memory and logic devices, biochemical sensors, and spin based solar cells. (Subproject-1)

Part-1 Molecular Spintronics Based Logic and Memory Units for Futuristic Computers

• Can molecules be the logic and memory devices of future?
• The concept of utilizing molecules as a logic device was proposed in the 1950s when modern computer was in their infancy. In the late 1980s, the discovery of Nobel Prize-winning spintronics devices showing two resistance states for the binary operations with a ferromagnet-nonmagnet-ferromagnet has revolutionized our data storage capacity and almost each of us are using spintronics in our modern-day computer hard drive.
• Spintronics (acronym of spin+electronics) opened new frontiers to harnessing spin properties of electrons as compared to electronic charge, for discovering futuristic logic and memory devices. Electron spin can be manipulated with low energy input to yield different resistance states without generating high heat. In traditional electron charge based devices high energy input and large heat generation are limiting the future possibilities of packing higher number of binary device/area.
• Interestingly, transferring the role of nonmagnet section of the ferromagnet-nonmagnet-ferromagnet based traditional spintronics device to a molecular channel produce a brand-new field of molecular spintronics. Molecular spintronics devices can harness molecular quantum states for enabling advanced memory operation, quantum computation and exploring multi-state logic devices to pack more computational power/unit area as compared to binary computer devices. However, integrating molecules into devices could not progress beyond the stage of experimental demonstrations. Due to extreme technological challenges, conventional low-yield and defect prone molecular device fabrication approaches focused on gold or nonmagnetic electrodes and simple molecules. Advancement in molecular spintronics will require connecting high potential molecules such as single molecular magnets, porphyrin, single ion magnets with the ferromagnetic electrodes.
• To address technological challenges, Dr. Pawan Tyagi has initiated a magnetic tunnel junction(MTJ) based molecular spintronics approach (MTJMSA) (Fig. 1a). MTJMSA is only approach that allow molecules to bond with two ferromagnetic films and enable the use of:
• (i) different types of ferromagnetic alloys without oxidizing or etching them during fabrication,
• (ii) different types of magnetic molecules without damaging them during fabrication and use,
• (iii) magnetic studies before and after coupling the molecules between two ferromagnetic electrodes ,
• (iv) robust and reproducible coupling between a magnetic molecule and ferromagnetic electrode with a linker,
• (v) high yield fabrication with commonly available microfabrication tools, and
• (vi) various control experiments to clearly distinguish response from molecule and artifacts.

We will utilize MTJMSA to harness and explore the device capabilities of high potential magnetic molecules like a single molecular magnet(SMM) for inventing futuristic computer devices (Fig. 1). SMM can transition among several quantum states (Fig. 1b-c) and may allow the realization of multiple device states. If MTJMSA show 5 states computational power of one future computer may become more than 1000 computers of present time. CREST grant will support the holistic exploration of the fundamental science of MTJMSA based unprecedented multi-state spintronics devices- that  may revolutionize future computer technology. MTJMSA offers endless innovation opportunities because number of molecules are endless J.

Can iron and nickel metal become solar cells?

A sustainable future will need cheap, highly efficient, and recyclable solar cells. It will be great if one can use iron as a solar cell material.

Our future research focuses on investigating magnetic tunnel junction(MTJ) as a solar cell. An MTJ utilizes nickel (Ni) and iron-like ferromagnets (FM1 and FM2). These ferromagnets undergo a dramatic change when strongly coupled via magnetic

Molecules. Our prior work on magnetic molecules created long-range effect on MTJ’s metallic electrodes that exhibited novel electronic and optical

Properties(e.g., Magnetic force image shows a part of the magnetic metal becomes nonmagnetic around the junction).

Preliminary MTJ based molecular device showed the intriguing photovoltaic effect. [1] (Ref. P. Tyagi and C. Riso, Nanotechnology, vol. 30, p. 495401, 2019).

We plan to study a wide variety of magnetic films and molecules. UDC is well equipped with micro-fabrication laboratory and collaborators.

New PhD students and collaborators interested in Renewable Energy are welcome to join this project in CNRE.

Can molecules in a magnetic tunnel junction(MTJ) based molecular device serve as a chemical sensor?

Defense and health-related systems may critically need chemical and biochemical sensors to accurately determine the threats to human life. This effort will produce a wearable  <0.5 mm highly sensitive, energy-efficient, and multi-chemical sensor.

Challenges: Our novel sensor will address the following questions.

• How to utilize a molecular spintronics device sensor, specifically designed for target molecules, to exhibit extremely high sensitivity detection
• How to utilize “one sensor” to detect multiple threat chemicals and biomolecules.
• How to miniaturize and remotely transmit data by inventing a suitable circuit, including a processor, an energy source and a transmitter.

Proposed Technical Approach: This future research will utilize molecular spintronics devices for sensing multiple chemicals. Our devices will be produced by transforming a capacitor or magnetic tunnel junction into molecular devices (Fig. 1). Multiple molecular device elements will be chemically bonded between two metal films. These molecular sensing elements will be chosen to detect chemicals of interest. Interaction of the target chemical with the molecular device element will produce change in the capacitance and current via the molecular channels.

Potential advantages:

• Very high signal to noise ratio: Only few molecules can produce large signal.
• Ultra compact and light-weight: Can be worn as a ring or button. (Sensor body <hair thickness)
• Long life and reusable: Self-cleaning operation can rejuvenate molecular sensing units.
• Configurable: Same molecular electronics sensor approach can be adopted for newly detected threat, threat chemical. Just use new molecular device molecule for a new need.
• Economical production: Will utilize photolithography, thin film deposition, and chemical treatment to produce hundreds of devices at a time.